Responses of Green Leaves and Green Pseudobulbs of CAM OrchidCattleya laeliocattleyaAloha Case to Drought Stress

This study examined the responses of green leaves (GL) and green pseudobulbs (GPSB) of CAM orchid Cattleya laeliocattleya Aloha Case to drought stress. After being subjected to drought stress, the decrease in water content (WC) was much greater in GPSB than in GL, indicating that GPSB facilitated a slow reduction in the WC of GL. This finding was further supported by the result of relative water content (RWC) of GL, which started to decrease only after 3 weeks of drought stress. Decreases of midday Fv/Fm ratios of GL occurred in all plants. However, the degrees of decrease were much greater in drought-stressed GL than in well-watered GL. Reduced Fv/Fm ratio (<0.8) at early morning was observed in drought-stressed GL after 3 weeks of treatments. Decreases in total chlorophyll (Chl) content, electron transport rate (ETR), photochemical quenching, qP, and nonphotochemical quenching, qN, were severer in GPSB than in GL after drought treatment. CAM acidity was significantly lower in both GL and GPSB after 2 weeks of drought treatment compared to well-watered plants. However, decrease of CAM acidity was smaller in GL than in GPSB. These results suggest that both GL and GPSB of CAM orchid Cattleya plantswere susceptible to drought stress