LIGHT INTENSITY AND ACTIVITY OF TRYPSIN INHIBITORS IN AMARANTH LEAVES AND SEEDS

Abstract

The effect of exposing Amaranthus hypochondriacus plants to different levels of photosynthetic photon flux densities (PPFD) during
development was analyzed in this work. Mature plants exposed to full sunlight (38.8 mol m^-2 d^-1) had higher instantaneous rates of net CO₂ uptake (A_n), reducing sugars content and thicker leaves, but lower chlorophyll content and leaf number per plant than those developed under reduced levels of PPFD (19.4 and 12.8 mol m^-2 d^-1). A physiological response to varying levels of PPFD was the differential accumulation of trypsin inhibitors in leaves and seeds. Leaves from plants grown under full sunlight conditions, showed a significantly higher trypsin inhibitor activity than leaves from plants partially shaded with plastic nets. In contrast, seeds collected from plants fully exposed to sunlight, showed the lowest level of trypsin inhibitors and higher rates of germination than seeds produced by plants exposed to the lowest level of sunlight. The capacity of A. hypochondriacus to adjust its morphology and physiology in response to light indicates ecological plasticity that might be helpful to face both biotic and abiotic stresses during their development.