Boron Excess Imbalances Root/Shoot Allometry, Photosynthetic and Chlorophyll Fluorescence Parameters and Sugar Metabolism in Apple Plants

Boron (B) excess frequently impair plant performances and their productivity; in particular in arid and semi-arid environments. In the present experiment; hydroponically-grown ‘Granny Smith’ apple plants grafted on M9 rootstock were treated with optimal (25 μΜ) or excess (400 μΜ) B for 116 days to evaluate allometric responses of plants to B toxicity and to highlight physiological (photosynthesis and chlorophyll fluorescence) and biochemical (pigment content and sugar metabolism) responses of apple plants to B excess. Boron accumulated principally in top > middle > basal stems and leaves of high-B-stressed plants. Notably, the stem dramatically accumulated a higher level of B, as an attempt to preserve leaves, especially the youngest from further B accumulation. B accumulation seriously affected photosynthesis of younger leaves and caused both stomata (reduced stomatal conductance) and biochemical (reduction of apparent CO2 use efficiency and pigment content) limitations and altered the photochemistry and energy partitioning in photosystem II. Boron excess altered leaf sugar proportion; increasing the accumulation of non-translocating sugars such as glucose and fructose. Our dataset adds knowledge on the effect of B excess in apple tree and poses serious concerns about the possible effect of B in altering sugar metabolism; which, in turn, can strongly affect fruit production of this worldwide-cropped species.

Growth, Evapotranspiration and Mineral Content of Gerbera Under Combined Salinity and Excess Boron

Gerbera is a very important plant widely grown for cut flowers. To check the influence of salinity and boron excess in nutrient solution, nine treatments as factorial combination of three sodium chloride (NaCl) (1, 15 and 30 mM) and three boron (B) (0.1, 1 and 2 mM) concentrations in the nutrient solution were applied during the gerbera cultivation. The effects of experimental treatments on gerbera growth, flowering and the interaction in morphological and nutritional aspects were tested. The formation of leaves, stems and flowers, flower dry mass and evapotranspiration (ET) were more negatively affected when plants were irrigated with 2 mM B than with 0.1 mM B concentration. High levels of boron (1 and 2 Mm) in nutrient solution resulted in leaf chlorosis and necrosis. The severity of leaf burn was correlated with leaf B content. Salinity acted as a protector against boron content in leaves and flowers at 1 Mm B. However, at the 2 Mm B in nutrient solution, leaf B accumulation was not reduced by the presence of NaCl but also increased with the increased levels of salinity. The external levels of boron used in this study, which were found to be the highest in the literature, and the high sensitivity of gerbera to boron, suggested that boron acted as the dominant factor. Lower external boron concentrations would be needed to establish to what extent salinity would be able to mitigate the negative effects of boron.