Acclimatization physiology in tissue cultured plants
Physiological and morphological aspects of acclimatization were studied in cultured tomato (Lycopersicon esculentum Mill.), banana (Musa accuminata L.) and date palm (Phoenix dactyli/era ). The nutrient availability from agar solidified culture medium was determined to establish the nutrient status of the cultured plandets before transfer to ex vitro conditions. Analysis of the plant tissues demonstrated decreasing tissue concentrations of the major elements nitrogen, phosphorus and potassium with decreasing concentration of basal salts in the medium. The effects of agar and increasing sodium concentration in the culture medium was studied in cultured banana plants. Plandets grown on agar solidified medium with increased levels of sodium, exhibited reduced growth and stomatal movement. The use of agar as a solidifying agent was shown to reduce root growth, development and stomatal functioning in these plants. The efficiency of ion and water uptake, and translocation in in vitro and acclimatized tomato plants was assessed using [32P]-orthophosphate and [3H]_ tritiated water. The functional capacity of the root system fOlmed in vitro was established, and assessed following acclimatization treatments at 40% and 80% relative humidity. Comparative studies with tomato seedlings demonstrated reduced efficiency of ion translocation to the shoot in plandets growing in vitro. However, transport to the shoot improved during acclimatization. Ion absorption studies on in vitro and acclimatized palm plants demonstrated phosphate uptake and translocation in both plant types. A detailed examination of the tissue structure through the root/shoot junction and roots of · cultured, acclimatized and seedling tomato plants illustrated differences in the vascular development between the three plant types. However, no major abnormalities were observed which could have accounted for the reduced translocation efficiency in the cultured plants. Increased vascularization present in the root/shoot junction of the cultured plants may increase resistance to the transpiration flow through the region. The type of root system produced in vitro and the root/shoot ratio was manipulated using varying IAA and sucrose treatments. Improved root development and plantlet survival rates were achieved by reduced exposure to IAA during the root initiation phase followed by root elongation on IAA free medium supplemented with sucrose. Acclimatization at low relative humidity (40%) was achieved by producing plandets with balanced root/shoot ratios and a well developed root system.
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