Chlorophyll a fluorescence in response to phosphorus deficiency and heat stress

Photosynthesis and particularly photosystem II (PSII) is considered sensitive to high temperature. Our main objective in this study is to understand the role of phosphorus in heat treatment effects alleviation in tomato plant. In this work, the influence in three levels of phosphorus concentration (15, 31 and 60 ppm) assured by two forms of fertilisers (Mono-Ammonium Phosphate (MAP) (11-52-0) and NPK (15-15-15)) on tomato plants growth and heated-leaves treatment responses was investigated. Tomato plants were grown in hydroponic conditions and the effects of different P levels in change of chlorophyll content index, leaves dry weight and total P in root and shoot ratio were analysed. Results present that plants grown in low phosphorus concentration in hydroponic medium showed a decrease in chlorophyll content index, leaves dry weight and total root P/total shoot P ratio. Furthermore, heat treatment at 40 °C for 30 min significantly affects chlorophyll a fluorescence transient shape and photosynthetic performance index parameter (PIABS). We observed that the two forms of fertilisers positively alleviated the detrimental effects of high temperature on leaves of plants grown at high level of phosphorus. According to these results, the role of phosphorus in the alleviation of the effects of temperature on the electron transfer chain is observed. However, the mechanism by which P acts in this protection remains unclear. It is possible that P has a significant action at the level of the PSI, but further studies are necessary to elucidate the direct or indirect actions of P in this heat effect alleviation. Also, a combined action of P, N and other mineral elements is very likely in this protection against the negative effects of high temperatures.