How Do Different Watering Regimes Affect the Growth, Chlorophyll Fluorescence, Phytohormone, and Phenolic Acid Content of Greenhouse-Grown Ceratotheca triloba?
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We evaluated the effect of different watering regimes on the growth, chlorophyll fluorescence, phytohormones, and phenolic acids in Ceratotheca triloba (Bernh.) Hook.f., a commonly consumed African indigenous leafy vegetable. The study was conducted in the greenhouse under different watering regimes [seven (daily); three (thrice); two (twice); one (once) day(s) per week] for a period of 2 and 4-months. In each pot (7.5 cm diameter; 150 ml volume), 50 ml of water was applied per treatment. At the end of the experiment, plant growth, chlorophyll fluorescence, phytohormones, and phenolic acids were determined. A decrease in water availability resulted in a consistent decline in plant growth after a 4-month growth period. The severity of reduced water availability was more noticeable in plants watered once a week with a 1.4-fold reduction in growth and quantum efficiency of PSII (Fv/Fm) value of 0.80. The significant decline in growth and chlorophyll fluorescence was probably due to the increased production of abscisic acid (ABA) and cytokinin (CK) content together with the detected phytohormones in plants with restricted water supply. Furthermore, plants watered once a week had a trade-off between growth and phenolic acid production, with significantly higher (threefolds) concentrations of vanillic, ferulic, caffeic, and 4-coumaric acids in 4-month-old plants. Even though C. triloba grew best in well-watered soil, the plant had the potential to adapt and survive in soils with limited water supply for longer periods of growth. These findings suggest that regulation of phytohormones and phenolic acids played an important role in improving the growth of C. triloba under limited water conditions.
KeywordsAbscisic acid Cytokinins Phytochemicals Phytosynthesis Traditional leafy vegetable Water stress
We appreciate the financial support from the National Research Foundation (NRF, Grant UID: 89290), Graça Machel (Canon Collins) and the University of KwaZulu-Natal (Pietermaritzburg), South Africa. NAM and AOA thank the Stellenbosch University and North West University (Mmabatho) for provision of access to resources utilized during the preparation and revision of the manuscript. The Ministry of Education, Youth and Sport of the Czech Republic via National Program for Sustainability (Grant LO1204) and the Czech Science Foundation (Grant 14-17-06613S) are also thanked for their financial assistance. Prof R.P. Beckett (University of KwaZulu-Natal, Pietermaritzburg) is thanked for his assistance with chlorophyll fluorescence experiments.
NAM conceived the research idea, designed the study, conducted greenhouse experiments and quantified stress-related phytohormones. AOA, MGK, ON, JG, KD advised on relevant experimental design and experiments performed. JG as well as KD and MS provided equipment used for quantification of phenolic acids and phytohormones, respectively. AOA, IP, LP and MŠ assisted with the quantification of phytohormones. AOA provided technical assistance in the interpretation of the phytohormone and phenolic acid data. NAM prepared the manuscript while all authors edited and approved the final version. JFF and JVS coordinated and supervised the project.
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