How Do Plants Control the Shoot:Root Ratio

Both Carbon and Nitrogen are essential in plant development. The carbon is the fuel for cell division, growth and a respiratory substance and the Nitrogen enables amino acid production and DNA synthesis. In turn this growth causes the shoots and roots to extend and consequently there is normally a fixed ratio between how the plants allocate these resources.

The intimate association between these to essential compounds is effected by the way the plant acquires them. The Nitrogen enters the plant through the root in the form of Nitrates and the Carbon enters in the form of CO2 and is converted to sucrose: the photoassimilate. The Nitrates move up through the xylem from the, carried by the capillary action of the water. The sucrose, produced by photosynthesis, is exported into the phloem and is then transported down to the roots to enable sufficient metabolism in the light deprived areas of the plant. In general, the source for the Carbon is the sink for the Nitrogen and visa versa.

The Biochemical Basis of Plant Adaptations to Drought and Salinity

In a stochastic environment, plants' sessile nature means that variations in water availability have detrimental effects on the plants metabolism. The availability of water for its biological roles as a solvent and transport medium, as an electron donor in the Hill reaction, and as an evaporative coolant is often impaired by environmental conditions such as drought and salinity. The oxidative stress that results from these environmental perturbations has profound biochemical responses within the plant's genetic architecture. As both these stresses impact on the water availability of the organism, they will share many response mechanisms despite being fundamentally different stimuli.

Both drought and salinity stress the cells by increasing the concentrations of ions in the cytosol. Increased ion concentrations can have osmotic effects causing the plant to lose control over water flux; furthermore, high concentrations of ions have extremely negative impacts on the tertiary structure of proteins, which form the basis of all cellular machinery.