Genetic analysis of structure and function of stipules in pea (Pisum sativum)

Abstract

To reveal the role(s) of stipules, pea genotypes of nearly common genetic background, but differing in the combination of wild type and mutant alleles of STIPULE-REDUCED, AFILA and TENDRIL-LESS genes together with COCHLEATA gene, were grown in a field in completely randomized design during the winter-spring seasons through 2006 to 2011 at the farm of the institute. The genotypes were characterized organ-wise, for morphological and anatomical features, photosynthesis and biomass accumulation and partitioning. Stipules were found similar to leaves/leaflets in respect of stomata shape, size and frequency as well as size and shape of pavement cells in epidermis and internally, in possession of palisade- and spongy-mesophy 11 parenchyma and veins in high density. In contrast to leaflets, which possess single primary vein and smooth lamina margin, the stem proximal part of stipule had serrations and possessed several primary veins; however, its distal part had single primary vein and smooth lamina margin. Simultaneous occurrence of the properties of simple and pinnately compound and palmate lamina structure were identified in stipules. Compared to leaflets in which the highest order of veinal reticulation was quinternary that in stipule was sexternary. Stipules were highly effective photosynthetic organ, responsible for about 30% of photosynthesis in phytomeres. Stipules enlarged plant's photosynthate/biomass production and accumulation capacity by about 72%. The presence of stipules avoided feedback inhibition of photoassimilation in leaves, by ensuring that pods/seeds remained the principal sink for photoassimilates. The presence of stipules was essential for high harvest index and grain yield; the harvest index in the stipule-deficient genotypes was 2.8 fold lower as compared to genotypes possessing wild type stipules. The plants in which the stipules were intact but leaves had been surgically removed, produced seeds proving that stipules alone were sufficient for survival and completion of life cycle in pea plant. The plants from which stipules had been surgically removed had reduced growth indicating that the presence of stipules was vital for continued shoot growth. The observations altogether demonstrated additive interaction between stipules and leaves in the accomplishment of photosynthesis, accumulation of biomass and the production of seeds in high yield with high harvest index. It was concluded that the presence of photosynthetically efficient stipules is a requirement in the breeding of high yielding cultivars of the pea (Pisum sativum) crop.