Water stress, rapid polyribosome reductions and growth.

Measurements of the water status of various plant tissues exposed to differing levels of salts for 1 hour were made using the recently developed Campbell J-14 press (Logan, Utah). Values obtained with the press were found to correlate well with estimates of relative water content, and experiments with 3-day-old pumpkin seedlings showed that detectable changes in press values of cotyledon tissues could be obtained within 5 minutes following salt- or desiccation-induced stress.Polyribosome levels were measured in tissues from various plant species following short duration water stress. A small reduction in polyribosome percentage was obtained in cotyledons of 3-day-old pumpkin seedlings which were exposed to an osmotic potential (NaCl) of -4 bar for 10 minutes, but more pronounced changes were found after 30 minutes of stress. Shoot tissues of peas, barley, wheat, and safflower following 20- or 30-minute salt- or desiccation-induced stress yielded extracts with reduced polyribosome levels; however, 30 minutes of exposure of cotton and pumpkin seedlings to -6 bars did not result in altered polyribosome percentage of extracts from roots. Studies using shoot tissues from pumpkins and peas showed that polyribosome percentages and growth rates of both plants were reduced in proportion to loss of tissue water. These plants differed in their sensitivity to stress in that polyribosome content and growth rate reductions were both nearly twice as severe per unit of water loss in peas as in pumpkins. These data along with those obtained by others suggest that growth rate reductions may be directly proportional to reductions in polyribosome levels during water stress.