Contrasted Effects of Prolonged Root Hypoxia on Tomato Root and Fruit (Solanum lycopersicum) Metabolism

The decrease in growth rate of the root system, or the complete cessation of its growth, in fruiting tomato plants is a known phenomena. It has been suggested that a limited supply of carbohydrates to this organ, because of its relative weakness in competition with the developing fruitlets is the main cause for these disorders. This hypothesis was tested in this study with tomato plants ( Solanum lycopersicum cv Micro-Tom) submitted to gradual root hypoxia (1–2 % oxygen) at first flower anthesis and with limited fruit number (six fruits per plant). To this end, a range of physiological and biochemical parameters was evaluated. Our results showed that under oxygen deficiency, root growth was severely affected. In contrast to fruits, root protein and carbohydrate contents decreased significantly, concomitantly with a significant decrease in photosynthesis. Together the present data revealed that, at the fruiting stage, the effect of flooding on root growth and metabolism is probably controlled by the relative sink strength of the fruit.     

Does the source of nitrogen affect the response of subterranean clover to prolonged root hypoxia?

Nitrogen (N) is taken up by most plant species in the form of nitrate (NO ) or ammonium (NH ). The plant response to continuous ammonium nutrition is species‐dependent. In this study, the effects of the source of N nutrition (NO , NH , or the mixture of NO and NH ) on the response of clover (Trifolium subterraneum L. cv. 45C) plants to prolonged root hypoxia was studied. Under aerobic conditions, plant growth was strongly depressed by NH , compared to NO or mixed N nutrition, as indicated by the significant decrease in root and shoot‐dry‐matter production (DW), root and shoot water contents (WC), leaf chlorophyll concentration, and chlorophyll fluorescence parameters (F₀, F_v/F_m). However, the N source had no effect on chlorophyll a–to–chlorophyll b ratio. Under hypoxic conditions, the negative effects of root hypoxia on plant‐growth parameters (DW and WC), leaf chlorophyll concentration, and chlorophyll fluorescence parameters were alleviated by NH rather than NO supply. Concomitantly, shoot DW–to–root DW ratio, and root and leaf NH concentrations were significantly decreased, whereas root and leaf carbohydrate concentrations, glutamine synthetase activities, and protein concentrations were remarkably increased. The present data reveal that the N source (NO or NH ) is a major factor affecting clover responses to hypoxic stress, with plants being more tolerant when NH is the N form used. The different sensitivity is discussed in terms of a competition for energy between nitrogen assimilation and plant growth.