Physiological changes and growth of micropropagated chile ancho pepper plantlets during acclimatization and post-acclimatization

Little is known about physiological changes that occur with micropropagated chile ancho pepper (Capsicum annuum L. cv. San Luis) plantlets during accl imatization. Plantlets were transferred to ex vitro conditions to study sel ected physiological changes and growth performance during acclimatization a nd post-acclimatization. The physiology of the plantlets was characterized by measuring leaf gas exchange and water status. Plant growth was determine d by assessing plant height, leaf number, total leaf area, relative growth rate (RGR), and leaf, root, and stem dry matter (DM). Chile pepper plantlet s became acclimatized within 6 days after transplantation. During this peri od, physiological adjustments occurred, which were critical for plantlet su rvival. After initial ex vitro transplanting, plantlets experienced water d eficit [leaf wilting and reduced relative water content (RWC)], which corre sponded with reduced stomatal conductance (g(s)) and transpiration (E), and an increase in stomatal resistance (r(s)). Thus, leaf stomata that develop ed in vitro were functional ex vitro. Because of this stomatal control, pla ntlets minimized transplant shock, recovered and survived. Prior to transpl anting, plantlets were photomixotrophic, as indicated by low photosynthetic rates (A). During acclimatization, RWC, g(s), E, and A were significantly lower two days after transplanting. However, within 6 days after transplant ing, plantlets recovered and became photoautotrophic - attaining high A, g( s), and E. Water use efficiency was initially low during the first days aft er transplanting, but increased dramatically at the end of the acclimatizat ion period in part due to increased A. The stabilization and improvement of plantlet water status and gas exchange during acclimatization and post-acc limatization closely correlated with increased plantlet growth.