EFFECTS OF WATER-DEFICIT STRESS ON THE DEVELOPMENTAL GROWTH OF EXCISED TOMATO ROOTS CULTURED IN-VITRO

Excised tomato roots (Lycopersicon esculentum Mill. cv Bonny Best) wer e cultured in the presence of mannitol to determine the effects of var ying degrees of mild water deficit on their developmental growth. It w as found that over the 7-d culture period, the cultured roots could re gulate their own developmental responses to the water deficit such tha t elongation of the primary root axis was favored over that of the lat eral roots. Higher degrees of water deficit proportionately decreased lateral root number and density, but lateral root primordia (visualize d by clearing roots in chromium trioxide) continued to be formed in wa ter-stressed roots. Measurements of water and osmotic (solute) potenti als of the root tips showed that the cultured roots osmoregulated and did not suffer a loss in turgor pressure as a result of the mannitol t reatments. However, reciprocal transfer experiments showed that root c ultures were unable to resume growth after removal from water deficit conditions, thus indicating a probable requirement for the shoot for c omplete recovery.