BORON DEFICIENCY AFFECTS GAS EXCHANGE AND PHOTOCHEMICAL EFFICIENCY (JPI TEST PARAMETERS) IN GREEN DWARF COCONUT

Abstract

Boron (B) deficiency causes a wide array of symptoms, not only among species of palms, but also within a single species (i.e. Cocos nucifera). A better understanding of the effects of B deficiency in coconut will be important to try optimizing a rational fertilization management in coconut plants. Thus, modification of PSII photochemistry (using a group of fluorescence parameters, called the JIP- test, that quantify the stepwise flow of energy through Photosystem II) and gas-exchange in boron deficient green dwarf coconut plants were investigated. Our results suggest that a modification of PSII photochemistry (non-stomatic effects) and gas-exchange (stomatic effects) were induced by boron deficiency. Such modifications are manifested by (1) increase the ratio of total dissipation to the amount of active reaction centers (RCs) [dissipation (DI)/RC] and (2) leaf-to-air vapor pressure difference (VPD_leaf-air). These modifications (on PSII photochemistry and gas-exchange) were caused by a decrease in energy absorbed per excited cross-section [absorption flux (ABS)/cross section of the sample (CS₀)], density of active reaction centers (RC/CS), maximal trapping rate of an exciton that will lead to Q_A reduction measured over a cross- section of active and inactive RCs [trapping flux (TR)/CS₀], electron transport per excited cross-section [electron transport flux (ET₀)/CS)], area above curve (proportional to the pool size of the electron acceptors QA on the reducing side of PSII), photosynthesis (A), stomatal conductance (g_s), transpiration (E), chlorophyll concentration (SPAD readings), growth parameters (root DW and height plant). Our results demonstrate that by analyzing fluorescence (JIP test parameters) derived from the polyphasic fluorescence transients measurements were able to estimate the functional changes of PSII in B deficient coconut plants. The results in this study suggest that fluorescence analysis (JIP test) and instantaneous measurements of gas-exchange can be useful tools in assessing the physiological effects of B deficiency in green dwarf coconut.

Keywords:

• boron
• plant physiology
• photosynthesis
• tropical crops

ACKNOWLEDGMENTS

The authors would like to thank Dr. Timothy K. Broschat, Professor of Tropical Ornamental Horticulture at the University of Florida's Fort Lauderdale Research & Education Center for helpful discussions and grammar correction. The authors wish to thank also Professor Reto Jörg Strasser, Head of Bioenergetics Laboratory, Laboratoire de Bioénergétique, Université de Genève, Switzerland, for their invaluable assistance regarding use of the Biolyzer software. The authors thank National Council for Scientific and Technological Development (CNPq, Brazil) for the fellowships awarded to E. Campostrini.