PJB-2019-916
EFFECTS OF CALCIUM ON PHYSIOLOGY AND PHOTOSYNTHESIS OF of Paris polyphylla Sm. UNDER HIGHT TEMPERATURE AND STRONG LIGHT STRESS
pengyao
Abstract
The present study aimed to explore the feasibility of application of exogenous Ca2+ to alleviate the damage caused by high temperature and strong light stress of Paris polyphylla (P. polyphylla) by analyzing the effects of different Ca2+ concentrations on photosynthesis, stress resistance, and several physiological parameterss of P. polyphylla under high temperature and strong light stress. The multi-flowered P. polyphylla plants with shading treatment were used as the experimental material and cultured with a modified Hoagland solution. The Ca2+ concentrations in the culture medium were set as 10, 14, 18, 22, and 26 (mmol/L), respectively. The shading shed was removed and the stress treatment was carried out before the approaching of high temperature and strong light stress. After 10 days of stress treatment, the photosynthesis rate and physiological parameters of P. polyphylla were measured. After the death seedling of P. polyphylla, the root and stem/shoot yield and the content of active ingredient were determined. In the study, two normal controls were set, one is shading at normal temperature (25°C) and other is spraying Hoagland solution under high temperature and strong light stress. The results showed that Ca2+ treatment with the appropriate concentration significantly enhanced the activities of peroxidase (POD), superoxide dismutase (SOD), and catalase (CAT) in the leaves of P. polyphylla, reduce the contents of O2-• and H2O2 in cells, decreased the content of malondialdehyde (MDA) and the relative conductivity, and effectively alleviated the damage caused by stresses of strong light and high temperature.. Furthermore, Ca2+ treatment also increased chlorophyll content, stomatal conductance, contents of soluble protein and proline, and accelerated photosynthetic electron transport, reduced non-photochemical quenching (NPQ), and improved the actual photochemical efficiency, electron transport rate (ETR) and photochemical quenching index (qP) of photosystem II (PSII), making P. polyphylla to maintain a high net photosynthetic rate (Pn) under stresses of strong light and high temperature. However, as the concentration of Ca2+ increased, the capacity of P. polyphylla to resist stress was decreased. We found that 18mmol•L-1 Ca2+ treatment could significantly reduce the damage caused by high temperature and strong light stress to P. polyphylla, and increased its root and stem/shoot yield and the content of saponin.
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