Respiration hastens maturation and lowers yield in rice

Abstract

Role of respiration in plant growth remains an enigma. Growth of meristematic cells, which are not photosynthetic, is entirely driven by endogenous respiration. Does respiration determine growth and size or does it merely burn off the carbon depleting the biomass? We show here that respiration of the germinating rice seed, which is contributed largely by the meristematic cells of the embryo, quantitatively correlates with the dynamics of much of plant growth, starting with the time for germination to the time for flowering and yield. Seed respiration appears to define the quantitative phenotype that contributes to yield via growth dynamics that could be discerned even in commercial varieties, which are biased towards higher yield, despite considerable susceptibility of the dynamics to environmental perturbations. Intrinsic variation, irreducible despite stringent growth conditions, required independent validation of relevant physiological variables both by critical sampling design and by constructing dendrograms for the interrelationships between variables that yield high consensus. More importantly, seed respiration, by mediating the generation clock time via variable time for maturation as seen in rice, directly offers the plausible basis for the phenotypic variation, a major ecological stratagem in a variable environment with uncertain water availability. Faster respiring rice plants appear to complete growth dynamics sooner, mature faster, resulting in a smaller plant with lower yield. Counter to the common allometric views, respiration appears to determine size in the rice plant, and offers a valid physiological means, within the limits of intrinsic variation, to help parental selection in breeding.

Phenotyping for Nitrogen Use Efficiency: Rice Genotypes Differ in N-Responsive Germination, Oxygen Consumption, Seed Urease Activities, Root Growth, Crop Duration, and Yield at Low N

“…Germination, which is the most direct means to examine the meristematic behavior, has not been systematically examined as a phenotypic differentiator of any quantitative trait including NUE, despite the evidence that germination rate was tightly correlated with flowering time and yield in rice ( Sitaramam et al, 2008a ). Hence, the present study sought to explore N-responsive differences in germination and used them to identify contrasting rice genotypes that differed in N-responsive yield and therefore NUE.…”

“…This could be due to the prevailing notion that oxygen consumption (photo oxygen consumption or otherwise) has an opposing influence on yield or is at least a confounding variable as it counteracts the conservation of the photosynthate exclusively toward yield. Sitaramam et al (2008a) showed that meristem is a key determinant in the yield of rice, by demonstrating that the meristematic oxygen consumption hastens the life stages leading to less “time” available for accumulation of the photosynthate. They also showed that fast germinating rice genotypes have higher rates of oxygen consumption and mature faster with lesser grain yield, offering a testable paradigm of the role of energetics in plant yield, under which the role of nitrogen in the process could be studied.…”

“…Seeds of the selected rice genotypes were weighed individually and only seeds of modal weight were used as described earlier ( Sitaramam et al, 2008a ) for all experiments. They were surface-sterilized with 0.1% mercuric chloride for 50 s followed by 8–10 washes with double distilled water.…”

“…Oxygen consumption, which drives seed germination, is considered to affect biomass and therefore yield, as it uses up the photosynthetic reserves ( Cannell and Thornley, 2000 ). On the other hand, considerable clarity was obtained on the role of oxygen consumption vis-à-vis yield; the mechanism involves oxygen consumption driven acceleration of the meristematic growth (starting with germination), which in turn hastens the life cycle such as branching, such that the plant matures faster and yield is lowered due to shortened life span of the photosynthetic plant ( Sitaramam et al, 2008a ). Thus, oxygen consumption affects yield through controlling the life cycle, starting with germination and branching upto flowering and yield.…”

The place of education/learning in the hierarchy of Engels’ curves of consumption: the quantitative basis of mechanisms finally elucidated.

“…Since no standard remedy exists, we even tested this procedure of uniform sampling in the case of rice seeds by their weight in our earlier studies to predict yield in a single day from the seeds successfully [54]. Clearly, if the procedure is haphazard or without coherence in logic or sampling, the ensuing results would be even worse and it would be the ultimate verdict against the validity of the method.…”