EFFECTS OF LIGHT AND GROWTH-REGULATORS ON GERMINATION AND RADICLE GROWTH OF LETTUCE SEEDS HELD UNDER HIGH-TEMPERATURE STRESS AND WATER STRESS

Seeds of two cultivars of lettuce (Lactuca sativa L.), untreated or soaked in acetone containing kinetin and gibberellic acid (K + GA3), were germinated in light or dark at a range of (high) temperatures and at a range of water potentials. In addition, untreated and treated seeds were germinated at 20°C in the light and then transferred to the same high temperatures or to low water potentials. In both cvs light and K + GA3 promoted germination at high temperatures and at low water potentials, although the cvs differed quantitatively in their responses. The upper temperature limit of germination in the light, and of radicle growth after germination, were similar in treated and untreated seeds respectively, suggesting that light and K + GA3 in combination may have completely removed the specific high‐temperature block to germination. Although light and K + GA3 increased the tolerance of germination to water stress, germinated, untreated seeds were able to grow at even lower water potentials. The K + GA3 treatment, whilst promoting germination under high temperature or water stress, reduced radicle growth subsequent to germination, thus providing support for the possibility that, in germination, the initiation of cell elongation has a degree of metabolic independence of the other processes associated with growth. Copyright © 1979, Wiley Blackwell. All rights reserved