The effects of water deficit on growth, photosynthesis and protein synthesis of selected woody ornamental species

Abstract

Seven woody landscape ornamentals were grown in a glasshouse under wellwatered conditions and screened for water consumption, net assimilation rate (NAR) and water use efficiency. Lagerstroemia indica 'std. purple' L had the highest water consumption over a 73 d period. When whole plant transpiration (T) was expressed on a leaf area basis Sophora secundiflora Ort. had the highest T. By covering the medium with polyethylene, water loss through the soil was prevented and savings of 12 to 88 % were observed without affecting growth. Lagerstroemia had the highest net assimilation rate and W U E of all species tested. Water use efficiency was lowest in Sophora. Sophora (high T, low WUE), Lagerstroemia (Moderate T, high WUE), and Pittosporum tobira Thunb. (low T, high WUE), were grown in a growth chamber and water deficit imposed by withholding water. Based upon the xylem water potential (XWP) at which carbon exchange rates (CER) were depressed to levels below control plants, Lagerstroemia was considered to be the most sensitive to water deficit. Growth rates, as measured by leaf expansion, were not sensitive indicators of water deficit in Sophora and Pittosporum, but were in Lagerstroemia. To maximize CER, irrigation could be scheduled by monitoring XWP or stomatal conductance which could make the most efficient use of increasingly scarce water resources. Protein synthesis and leaflet content of protein were not affected by water deficit No differences were observed in protein patterns between control, mild (MWS) and high (HWS) water stressed plants when one-dimensional SDS-PAGE were run. However, polypeptide synthesis, as visualized by two-dimensional PAGE, was dramatically affected as water deficit progressed. Generally, polypeptides between 48-66kD and pH 5.2-6.5 decreased with decreasing XWP but reappeared upon rewatering. Three polypeptides with M (subscript r) from 23-25 kD were uniquely present at -2.0 MPa but upon further water deficit, disappeared. The differential expression of these polypeptides in response to water deficit may enable Sophora to continue growth and CER at lower XWP.