A rapid, reproducible, non-destructive tissue generation protocol was a fundamental requirement for studies of the mechanism of suboptimal temperature stress in photosynthetic cotton seedlings. An absorbent paper scroll technique adapted from seed quality testing produced a homogeneous population of 10-day-old, autotrophic seedlings which were exposed to 10, 15, 20, 25, or 30 C on Days 4 through 10, Days 4 through 8, or Days 9 through 10. The seedlings exposed to 10, 15, 20 or 25 C on Days 4 through 8 were allowed to "recover" at 30 C on Days 9 through 10.

In metabolic and ultrastructural studies, use of classical growth parameters [root, shoot and seedling lengths and dry weights] was precluded by seedling stress responses [excessive root branching and/or hyperelongation], insufficient sensitivity within experiment time-frame, and tissue destruction (1). Root and shoot fresh weights of the adequately hydrated seedlings generated in this pseudo-hydroponic system proved to be accurate indicators of optimal root and shoot growth temperatures and rapid, sensitive, and reproducible measures of stress response in three cotton cultivars [as well as other oil seedlings, e.g. cucumber, cantaloupe, sunflower and watermelon (2)].

In cotton (Paymaster 145, Coker 315, and Deltapine 61] and the other oil seedlings, varietal differences were observed in the degree of fresh weight reduction induced by moderate chilling. More significantly, the capacity to return to pre-stress status differed among the oil seed cultivars and species. In sunflower and the cucurbits, recovery capacities were related to suboptimal temperature resistance (2). This relationship appears to extend to cotton.

Determinations of the relative water contents [RWC] of roots and shoots from stressed and unstressed oil seedlings showed varietal differences in both the significant interaction between temperature and seedling water status and the capacity of the seedlings to return to pre-stress water status when restored to promotive growth temperatures. The different varietal responses in the destructive RWC determinations correlated with those obtained through simple root and shoot fresh weights measurements.

The well-known temperature sensitivity of germinating cotton seeds [and other species utilizing the glyoxylate respiratory shunt] persisted in photosynthetic seedlings. Cultivar differences in degree of response to moderate chilling stress were observed, and the capacity to regain pre-stress water status is an important factor in moderate-chilling "sensitivity".