Effects of Water and Nutrition on Photoassimilates Partitioning Coefficient Variation

International audiencePhotoassimilates partitioning was studied using the experimental data of winter wheat in 2008-2009 at irrigation experimental station of Tianjin Agriculture University.The Research showed that when relative development stage (RDS) was greater than 0.35 fr(root), fr (stem and sheath) and fr(leaf) decreased ,fr(Ear) increased with the increase of RDS,and turned into negative When RDS were 0.59,0.67,0.7 respectively.It was due to the existence of repartitioning of photoassimilates, and photoassimilates storaged in root , stem and sheath and leaf began to transport to ear.Water and nutrition had a certain influence on the partitioning of photoassimilates among organs.Excessive water and nutrition were unfavourable for the transportation of photoassimilates to the growth center

Rapid cooling triggers forisome dispersion just before phloem transport stops

Phloem transport stops transiently within dicot stems that are cooled rapidly, but the cause remains unknown. Now it is known that (1) rapid cooling depolarizes cell membranes giving a transient increase in cytoplasmic Ca(2+), and (2) a rise of free calcium triggers dispersion of forisomes, which then occlude sieve elements (SEs) of fabacean plants. Therefore, we compared the effects of rapid chilling on SE electrophysiology, phloem transport and forisomes in Vicia faba. Forisomes dispersed after rapid cooling with a delay that was longer for slower cooling rates. Phloem transport stopped about 20 s after forisome dispersion, and then transport resumed and forisomes re-condensed within similar time frames. Transport interruption and forisome dispersion showed parallel behaviour--a cooling rate-dependent response, transience and desensitization. Chilling induced both a fast and a slow depolarization of SE membranes, the electrical signature suggesting strongly that the cause of forisome dispersion was the transient promotion of SE free calcium. This apparent block of SEs by dispersed forisomes may be assisted by other Ca(2+)-dependent sealing proteins that are present in all dicots

Mechanistic modelling of carbon partitioning

Carbon partitioning between alternative sinks is the weak point of all plant growth models, being done using empirically based algorithms. While this approach is effective for simulations, it is unreliable for extrapolation to new conditions, and cannot provide mechanistic understanding of the processes involved. All long-distance carbohydrate transport and partitioning involves the phloem, hence partitioning must be a property of phloem physiology. However, no growth model utilizes the known phloem physiology. Relevant aspects of phloem physiology are discussed and used to produce a minimalist Münch-based flow model. This model provides a theoretical basis for an unambiguous definition of sink strength, with sink priority being an emergent property of the model. A method to extend this minimalist model is discussed