SciWhys: Why are plants green?

By Jonathan Crowe

After the greyness of winter, the arrival of spring is heralded by a splash of colour as plants emerge from the soil, and trees seemingly erupt with leaves. Soon, much of the countryside has moved from being something of a grey, barren wasteland to a sea of verdant green. But why is it that so much vegetation is green? Why not a sea of red, or blue? To answer this question let me take you on a colourful journey from the sun to within the cells of plant leaves.

As humans, our waking hours are punctuated by mealtimes: we must consume food on a regular basis if our bodies are to be able to generate the energy we need to survive. Plants, however, fuel their survival in an altogether different way. Plants don’t need to ‘eat’ as such; instead, they generate their own food supply. This manufacturing of food is powered by energy that plants capture from sunlight.

It might seem odd to say that sunlight contains energy, but our everyday experience shows this to be so: if we sit outside on a sunny day, our skin quickly becomes warm. This warmth is the result of our skin cells absorbing the energy contained in the rays of sunlight.

Read full article: SciWhys: Why are plants green?

High construction cost for cycads

Thomas Marler recently published the results of his research that reveal some of the attributes of the long-lived leaves of Guam's Cycas micronesica plants. "These leaves are relatively large and are constructed of tough tissues," said Marler. "Both of these factors indicate the construction costs of this leaf form are substantial."

Green leaves must pay back their own construction costs, but each leaf is also required to supply the energy needed to maintain its live tissues throughout its lifespan. Additionally, large plants like Guam's Cycas have an abundance of non-green tissue that requires energy to maintain. Therefore, large plants with this leaf construction strategy must also possess a payback strategy that allows recovery of these costs coupled with an excess in food synthesis to support plant growth. Read more> High construction cost for cycads

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Virus-resistant grapevines that make antibodies

Ask any group of agriculturists what one of his worst nightmares is, and the answer may well be "plant viruses." Unlike insect pests and weeds, which are relatively easy to control with pesticides and herbicides, plant viruses are largely resistant to chemical treatment.

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Virus-resistant grapevines that make antibodies

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Plant proteins block invading microbes

DAVIS, Calif., July 7 (UPI) -- U.S. and Danish scientists say they've identified proteins that prevent bacteria from infecting a plant's leaves.

The researchers at the University of Copenhagen, the University of California-Davis and UC-Berkeley said identifying the proteins will likely find application in better protecting agricultural crops and horticultural plants against diseases.

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Effects of Elevated CO2 on Rice Leaves

ReferenceLi, J.-Y., Liu, X.-H., Cai, Q.-S., Gu, H., Zhang, S.-S., Wu, Y.-Y. and Wang, C.-J. 2008.

Effects of elevated CO2 on growth, carbon assimilation, photosynthate accumulation and related enzymes in rice leaves during sink-source transition. Journal of Integrative Plant Biology 50: 723-732.

What was done
The authors measured several physiological processes -- including dynamic changes in photosynthesis and photosynthate accumulation, as well as enzyme activities such as sucrose phosphate synthesis (SPS) and sucrose synthase (SS) and their specific gene (SPS1 and RSus1) expressions -- in both mature (leaf 6) and developing (leaf 7) foliage of plants growing hydroponically in nutrient solutions within controlled-environment chambers maintained at atmospheric CO2 concentrations of 350 or 700 ppm throughout the entire week of leaf 6 development and expansion.

What was learned
Li et al. determined that "elevated CO2 significantly increased the rate of leaf elongation and biomass accumulation of leaf 7 during the treatment without affecting the growth of leaf 6." Over days 4-7, for example, the net photosynthetic rates of the mature leaves were increased by an average of 15% by the CO2 enrichment provided them, while the mean dry weight of the developing leaves in the CO2-enriched air was 100% greater than it was in the developing leaves in ambient air on day 2, dropping to 50% greater on day 3, and leveling out at 15% greater on days 5-7, equivalent to the same stimulation provided concurrently to the process of photosynthesis in the mature leaves. In addition, they say that in both developing and mature leaves, the net photosynthetic assimilation rate, all kinds of photosynthate contents (such as starch, sucrose and hexose), activities of SPS and SS, plus transcript levels of sps1 and RSus1, "were significantly increased under elevated CO2."

What it means
The seven researchers concluded that the "elevated CO2 had facilitated photosynthate assimilation, and increased photosynthate supplies from the source leaf [six] to the sink leaf [seven], which accelerated the growth and sink-source transition in new developing sink leaves." Put another way, mature rice leaves provide all sorts of CO2-enhanced help to developing leaves as the growth process proceeds; and they should continue to do so in an ever-increasing fashion as the air's CO2 content continues to rise, which is good news for rice ... and even better news for humanity.

Reviewed 17 June 2009