Position statement on Genetically Engineered Crops

The acreage used to grow GE crops has been on the rise, with nearly 167 million acres used to produce GE crops worldwide. According to the comprehensive global economic and environmental impact study of GE crops grown from 1996-2004, results are unambiguous that GE crops have the ability to confer herbicide tolerance and insect resistance. This has reduced the footprint of GM crops because of reduced pesticide application; however, this has also lead to an increase in herbicide use on HT crops and the subsequent emergence of herbicide resistant weeds. Thus, with respect to this issue, additional funding must be allocated to understand two concerns: the fate of toxins secreted in the soil that make crops IR and the physiological underpinning that renders a plant herbicide resistant. In addition, for such studies the plant protection quarintine (PPQ) should be adequately funded to conduct inspections at such sites with the possibility of developing a GPS coordinate database of all test sites.

However, it is important to note that these are input traits, developed with the goal of reducing or substituting agricultural inputs; these traits did not result in a marked increase in yield except in the case of IR Cotton. What benefit are such traits to growers who cannot afford high herbicide prices in developing countries where hunger is a pressing problem? In this area, it is important to fund a program, perhaps with a private entity, that will develop research insights into the genetic basis of abiotic stresses, in particular, drought and salinity tolerance. Such a program has the added benefit of less opposition from public policy circles in Europe since the chief objective is to develop a variety that is tolerant to abiotic stresses; moreover, on a long term note, with shifting climatic patterns, it is necessary to develop a genetic basis for improving crop production in areas of the world that will become more drought susceptible. Projects such as Golden Rice and rice engineered for trehalose production to render drought tolerance should be brought to fruition with a functional, focused relationship between public sector and private entity partnerships that are able to fund at least to the “scientific proof of concept” stage in field trials. This role should be adopted by the U.S. since it is uses nearly 55.3% (according to a 2005 estimate) of the global area used to produce GE crops

In addition to such efforts, emphasis (in terms of funding) should be placed on focused projects that are long term and comprehensive; for example, the effects of Bt pollen on stream ecosystems. It is important to build a database of ecosystem-level experimental findings so that we can analyze correlations and trends that develop as a result of using GE technology. To facilitate such studies and GE of novel crop varieties in general, initiatives such as the PIPRA deserve the cooperation of both public and private interested parties to streamline the process of licensing technologies to the private sector. In this way, common IP barriers will be less of an obstacle with more FTO and easier access to technology packages. The key drivers of this initiative should express particular interest in developing GE crops that are drought and salt tolerant.

In conclusion, my support for GE crops has a two pronged caveat: first, it is possible to maintain the competitiveness of the U.S. with GE input traits; in particular, beginning at the state level, several projects are at the gene discovery stage. Understanding the effects of these genes will be a useful tool for developing GE varieties that ward off disease or pests. However, at the global scale, it is important to take note of the intended actions of India for example—that will have the most stringent labeling policy. Could such a “precautionary” policy stance benefit the U.S. if one of the objectives of GE crops is to export the GE product with a stringent labeling policy? Second and finally, the development of a program lead by the U.S. that will oversee a streamlined approach to GE crops that are tolerant to abiotic stresses, with stronger international cooperation from private and public sector entities.

Leading Edge Vortices in Samara seeds

I knew that the physics of flight was an interesting area of research, but I did not know that it could be applied to an indehiscent dry fruit with wings: the samara. Dr. David Lentink, a professor from Wageningen University studies fluid mechanics of bird and insect flight; now, he has applied the concept of leading edge vortices (LEV) to the dispersal mechanism of plant seeds. In this sense, the body of scientific literature that supports the way fluid mechanics operates in a wide range of biological models gives renewed appreciation for the term ‘mechanism’ versus ‘phenomenon’ because too often we reduce the importance of motion in fluids, especially in the medium of air as mere phenomenon. Although much has been published in the area of biofluid mechanics in animal systems, research in plant fluid mechanics has been limited, probably in part because there are not many mobile elements in botany, at least at the macroscopic scale. Roots are solid anchors in the soil substrate and epiphytic plants firmly grip rocky landscapes. There are however, a group of winged seeds that rely on air movements to generate lift which in turn promotes their disperal; here, I examine the selective advantage of winged seeds to generate leading edge vortices as they descend-dispersing seeds in novel locations that will promote the successful transfer of genes to the next generation of winged-fruit trees.

Several factors influence the dispersal ability of winged seeds; some of these include the pattern or mode of flight. Some seeds have the ability to descend vertically while others either rock back and forth or spin about an axis as they generate lift on the leading edge of their papery wing (Minami and Azuma, 2003). Samara seeds tend to spin about a vertical axis as they begin flight. But what maintains lift at high altitutes? The location of the center of gravity on a winged seed is responsible for regulating two factors: the falling rate and the spin rate of the seed. A lead beading column was inserted and the regular roughness of the samara wing was filled in to shift the center of gravity on a modified samara seed. This had two couter effects compared with the normal samara seed: the spin rate decreased and the falling rate increased. In normal samara seeds, the spin rate is higher than the falling rate. Thus, the ability to disperse seeds is increased by increasing the stall time in air, that is, a higher spin rate to facilitate further distance of disperal. This was confirmed when cross sections of three regions of a natural samara seed were compared: a high degree of convex curvature is present at the base of the wing compared with the least curvature at the tip; the wing tip thus generates most of the lift.

Following the work of Yasuda and Azuma (1997), Dr. Lentink generated a vertical wind flow tunnel to determine how the angle of attack or coning angle (angle between the wing and the horizontal plane) changes with modified models of samara wings that have different leading edge configurations. Yasuda and Azuma (1997) determined that the coning angle varies between 47-53 degrees. How then, do samara seeds maintain lift at high altitutes with high angles of attack? Steven Vogel in Comparative Biomechanics suggests that samara seeds descend in an autorotating fashion; however, it is hard to visualize the motion as the seed descends along the vertical axis of rotation—Vogel terms this motion “wheeling”. This motion is possible because of the differential distribution of mass along the wing. In this sense, Karl Niklas in Plant Biomechanics suggests that an even distribution of mass along the wing would lead to a greater glide angle. This in turn would reduce the dispersal ability of the seed. Both Vogel and Niklas provide the common example of a flat piece of paper descending in flight—the flat piece of paper has to shift between various angles of attack as it glides through the air. By reducing the angle of attack, the unequal distribution of weight on a maple seed (the mass of the fruit) and the dynamic vortex generated at the wing tip promote greater disperal of the seed at a lower glide angle.

The unique dispersal capabilities of these helicopter seeds, so called because of the high vortices generated at the wing tip also have significant adaptive consequences in plant evolution. In plant evolutionary terms, the more fit individuals tend to be flowering plants or angiosperms because of their ability to exchange genetic information during pollination. The benefit from the added energy cost of this process? A developing embryo is protected within the walls of the flower’s ovary that eventually produces a mature fruit. On a geologic time scale, wing-seeded plants in the gymnosperm group of plants (non flowering, naked seeded plants with lesser zygote protection) represented a good percentage of the flora; after this period, pollination by insects replaced the need for dispersal by wind. This in turn fortified and selected for the mutualistic relationship between pollinators and their floral counterparts, with specialized floral phenotypes to attract select groups of insects. Thus, samara winged seeds possess a successful adaptive advantange over other flowering plants, in part because of one limiting factor that determines their dispersal ability: wind. At high wind speeds, winged seeds such as the samara are able to maintain a high spin rate and a lower falling rate at a low glide angle to achieve the maximum distance of dispersal from the source tree.

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Proper plant nutrition is important!

This semester, my undergraduate students and I developed nutrient solutions to grow plants hydroponically; that is, without a soil substrate. These included tomatoes, geraniums, sunflowers and yes, above all things, a weed-mint!

Nitrate Reduction in Response to CO2-Limited Photosynthesis

I. Research questions:

H1: How does CO2 stress affect nitrate uptake and reduction in maize?

H2: How does ‘H1’ affect carbohydrate levels and NRA?

II. Rationale:
Reduced CO2 concentration in the atmosphere limits the uptake of nitrate, its reduction to nitrite and ammonium and consequentially, the synthesis of amino acids.

III. Results:
Over a 10 hour treatment period, the amount of nitrate reduced (as a percent of uptake) was lower in CO2 – stressed seedlings. However, control plants (exposed to ambient levels of CO2 ) had a higher uptake, reduction and translocation of nitrate compared with CO2 – limited seedlings.

Although nitrate levels were similar at ambient and reduced CO2 in shoots, nitrate concentrations in the root at limited CO2 levels was lower than at ambient CO2 levels. This finding may be further fortified by the study on nitrate assimilation in perennial ryegrass. Both studies infer through different approaches, that there is reduced translocation of carbohydrates to the roots (because of increased leaf nitrate levels that sequentially inhibit sucrose phosphate synthase activity) and limited CO2 availability to drive nitrate reduction. Hence, as per Fig. 2D, there may be a reduction in root biomass at reduced CO2 levels (similar to the ryegrass study) and an elevation in nitrate levels may further depress translocation of sugars to the roots.

Of interest: nitrate levels in maize roots are higher than shoots. This differs from the findings of the ryegrass study—nitrate levels were higher in leaves. Moreover, the roots (as per Table I) appear to be the primary site of nitrate accumulation and reduced N. This is confirmed by a lower nitrate uptake and reduction among roots of intact and decapitated plants at low CO2 levels. However, it appears (according to Table II) that although roots may intercept and accumulate more nitrates than shoots, the overall shoot NRA is greater.

IV. Discussion questions/comments:

1) As per Table II, why is NRA greater in shoots (at both CO2 levels) while nitrate, soluble reduced N levels are greater in roots (Table I)?
2) Does the above question have to do with greater NRA in shoots because of amino acid formation etc?
3) Moreover, does maize maintain high root nitrate levels which then act as a signal to depress sucrose phosphate synthase activity and thus allocate amino acids toward the reproductive phase? Hypothesis: as a result, there is limited translocation of carbohydrates to the roots (such as in the ryegrass study). Maybe, maize can afford this since it doesn’t require additional root biomass—the roots are efficient at maintaining high nitrate and reduced N levels (Table I).

The site of nitrate assimilation and photosynthate partitioning between roots and leaves of the perennial ryegrass, Lolium perenne

The purpose of this study was to address two questions:

H1: Does reduced transport of photosynthates to roots correlate with an increase in leaf nitrate levels?

H2: Does photosynthate supply limit the capacity of roots to assimilate nitrate?

Rationale: Most trees synthesize amino acids in the roots. This suggests that the nitrate uptake efficiency of trees can be high; nitrate is transported to leaves and prior to abscission, the ion is stored in axial tissue for use during the following growing season (Larcher 1995). However, ryegrass accumulates nitrate in leaves; this acts as a signal to repress sucrose synthesis by favoring allocation of carbon toward amino acid synthesis and not carbohydrates. Thus, there is reduced transport of carbohydrates to roots and reduced root growth results in limited nitrate uptake.

Results: Ryegrass exposed to increasing nitrate levels in solution culture resulted in reduced photo-assimilated C (14C) allocation toward the root biomass. This was confirmed by an accumulation of nitrate in the leaves and reduced root biomass at high nitrate levels.

Moreover, NRA also increased in the presence of glucose while excised roots untreated with glucose showed no increase in NRA. However, with intact shoots and roots, NRA increased in leaves subjected to an enriched CO2 environment but there was no overall increase in NR root activity among all treatments. Moreover, among all treatments (enriched vs control CO2 and nitrate levels), roots have the least amount of 14C. Similar results were observed with the in vivo experiment with limited photo-assimilated carbon activity in the root.

Discussion questions/comments:

1) The authors suggest grazing can significantly reduce carbohydrates in the shoot biomass. Thus, there’s reduced availability of sugars at the root interface for nitrate assimilation. So, what is the purpose of evaluating responses to varying nitrate levels? Are nitrate concentrations more of a problem than grazing, or are the two issues related?

2) It seems nitrate levels are more of a concern. According to table 14, nitrate levels affected NRA activity; there was no significant increase in leaf NRA at high nitrate concentrations.

3) However, leaf nitrate levels increased with high nitrate concentrations. Nitrate is mobile in the plant and can be translocated via the dilute xylem sap. Can roots sense a high nitrate level in leaves and hence signal for reduced translocation of sugars to the roots since nitrate assimilation takes up nearly 25% of the energy generated by photosynthesis anyway?

4) Nitrate can have a high leaching potential in soil. What soil type does ryegrass usually grow in? Could ryegrass have evolved a mechanism for reducing sugar translocation in response to high soil nitrate levels?

5) Sugars can be important for translocating other ‘immobile’ nutrients such as Boron (in some species). Are there any deficiency symptoms observed in relation to reduced sugar translocation in ryegrass?

Elevated carbon dioxide levels negatively affect yield quality of wheat?

A plethora of reasons (such as industrialization and urbanization) have resulted in elevated CO2 levels in the atmosphere over time; as a consequence, plants have adapted by increasing biomass accumulation in response to an enriched CO2 environment. Thus, we are presented with the challenge of understanding the physiological responses of crops at an elevated CO2 concentration in the atmosphere. Wheat is one such important staple food source in many parts of the world. Wu et al. (2004) report the effects of elevated CO2 on wheat growth, water use efficiency[1], yield and its quality in response to two soil moisture treatments. This short critical review examines the purpose of the report, the experimental design, its salient results and the practical implications of the findings.

Wu et al. (2004) underscore the aim of their study as: the effects of two CO2 concentrations on the growth, yield (quality) response and WUE under two soil moisture levels. Specifically, the interactive effects of CO2 and soil moisture levels are analyzed for each response parameter (such as grains/plant, shoot weight, harvest index and WUE).

The experimental design includes two growth chambers (with ambient CO2 at 350 μl/l and elevated CO2 at 700 μl/l respectively), with controlled light, temperature (varied between day and night) and relative humidity levels. The wheat plants were subjected to two water levels (40% and 80% field water capacity, low and high moisture levels, respectively) in each growth chamber and harvested 93 days post-sowing.

Furthermore, on a critical note, it appears contradictory that Wu et al. (2004) vary the temperature in the growth chambers while maintaining a constant light level from 7.00 am to 7.00 pm at 450 μmol/m2/s. Solar energy is the source of energy that is converted to chemical energy in the photosynthetic process; moreover, solar energy is known to affect the temperature of ambient air. Thus, it appears unrealistic that the researchers would manipulate ambient air temperature to reflect field conditions while maintaining a constant PAR[2] for a 12 hour day period.

Elevated CO2 concentrations at both, low and high soil moisture levels result in increased plant growth. In particular, CO2 enriched Triticum aestivum plants at high moisture levels produced a significantly higher a) number of grains per plant and b) dry weight of grains per plant compared with the low moisture treated plants at ambient and elevated CO2 levels.
Of particular note, is the higher harvest index[3] among low soil moisture plants at ambient and elevated CO2 levels compared with high soil moisture plants. In addition, this correlated with a higher WUE for grain yield and shoot weight among low moisture plants compared with their high moisture counterparts. Wu et al. (2004) provide no explanation for their interesting result. In my opinion, it appears that the low moisture plants consume more water in order to produce some grain per plant at harvest; however, the high moisture plants produce a greater number of grains per plant under ambient and elevated CO2 conditions using a lesser amount of water. The low moisture plants, however, have to expend enough water to produce a fewer number of grains (compared with high moisture plants) while maintaining a higher harvest index. Thus, the shoot biomass allocated toward grain production is greater among low moisture plants at both CO2 levels.

Furthermore, CO2 enriched plants displayed reduced levels of protein, nitrogen, phosphorus, potassium and zinc compared with their ambient CO2 counterparts. This was accompanied by an increase in the starch content; however, a constant light level could have masked the actual nutrient level (increased starch could have diluted the nutrient composition) within the grains. Thus, Wu et al. (2004) argue that wheat plants exposed to high moisture and elevated CO2 levels use lesser water than their low moisture (implied in the context of a drought situation) counterparts to produce a greater grain yield. This study raises some important questions:

1) How do varying light levels affect the yield quality? Does this significantly alter the nutrient composition of the grains? If it does, additional experiments are required to confirm that elevated CO2 levels produce higher starch content in correlation with high moisture; the plants could have a relatively constant photosynthetic rate (inferred by the constant light level) and hence accumulate a greater proportion of starch in the grains.

2) What is the scientific basis behind the interactive phenomenon of soil moisture and elevated CO2 ? A proposed hypothesis: elevated CO2 levels are redistributing weather patterns (e.g., precipitation); hence, some regions of the world will become more arid than others. Moreover, is the interactive effect of increased CO2 and soil moisture a direct, immediate physiological effect or is the interaction between the two abiotic factors a long-term selection pressure that affects grain yield and quality?

[1] WUE: The water consumed per grain or shoot dry weight per plant
[2] PAR: Photosynthetically Active Radiation
[3] HI: The proportion of plant dry biomass allocated toward grains