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A 130-day hydroponic experiment was carried out in a glasshouse to examine whether manganese (Mn) concentration in the nutrient solution affects the nutritional status of olive plants and to find out whether the chlorophyll fluorescence technique is suitable to assess Mn toxicity and/or deficiency stress in olive plants prior to the appearance of these two nutritional disorders. For this purpose, chlorophyll fluorescence parameters (Fv/Fm and Fv/F0 ratios) were recorded every 40 days in the leaves of 'Kothreiki' and 'FS-17' olive cultivars, which were irrigated with Hoagland's nutrient solutions containing various Mn concentrations. In parallel the elongation of the main shoot of all experimental plants, as well as the concentrations of Mn, iron (Fe), zinc (Zn), boron (B), phosphorus (P), calcium (Ca), magnesium (Mg), and potassium (K) in their leaves were recorded. The following Mn treatments were applied: 0 μM Mn (to induce Mn deficiency), 40 μM Mn (to promote normal growth), and 640 μM Mn (to induce Mn toxicity). Our results indicated that not only the rate of shoot elongation but also the fluctuation with time of the leaf concentrations of all determined mineral elements (except for Mn) was not significantly affected by the Mn concentration in the nutrient solution, irrespectively of the cultivar. This was not observed with regard to the time variation of the Fv/Fm and Fv/F0 ratios, where the values of these parameters were significantly reduced in the 640 μM Mn treatment at the 80th and 130th day of the experiment in both olive cultivars, compared to the relevant previous ones (those of the days 0 and 40th), something which did not happen in the other two Mn treatments (0 and 40 μM). However, in none of the two cultivars tested and in any of the three Mn treatments (0, 40 and 640μM) the Fv/Fm and Fv/F0 ratios did not drop below the critical values of 0.8 and 4, respectively, even at the end of the experiment, where high Mn concentrations were found in the leaves of both cultivars treated with 640 μM Mn (616 μg g-1 d.w. in 'FS-17' and 734 μg g-1 d.w. in 'Kothreiki'). Symptoms of Mn toxicity (curling and brown speckles) were observed in the top leaves of both cultivars, after the 90th day of the experiment. At the same time, the final leaf Mn concentrations (those of the 130th day of the experiment) in plants grown under 0 μM Mn were 23 μg g-1 d.w. in 'FS-17' and 20 μg g-1 d.w. in 'Kothreiki', i.e., a little above of the deficiency range (<20 μg g-1 d.w.). At the 130th day, Mn concentration in nutrient solution, as well as Mn concentration in the leaves of both olive cultivars was negatively correlated with the leaf concentration of Fe and the values of the Fv/Fm and Fv/F0 ratios, and positively with the concentrations of Zn and P in the leaves. Finally, the periodical measurement of the Fv/Fm and Fv/F0 ratios was proved to be a non-reliable means to predict the appearance of the visible symptoms of Mn toxicity in olive leaves (although their values declined significantly at the 80th and 130th day of the experiment in both olive cultivars). [ABSTRACT FROM AUTHOR]

A greenhouse experiment was carried out in order to study the effects of B excess (2.50 mg B l−1) on physiological (B concentration and distribution, gas exchange parameters, chlorophyll concentration and fluorescence) and anatomical (leaf structure and chloroplast ultrastructure) characteristics of ‘Navelina’ orange plants grafted on sour orange and Swingle citrumelo rootstocks. Boron concentrations of all plant parts increased with increasing B concentration in the nutrient solution, following the order: old leaves>young leaves>bark of rootstock>root>stems of scion>stem of rootstock>wood of rootstock. ‘Navelina’ plants were less sensitive to excess B when grafted on Swingle citrumelo than on sour orange. This was due to the lesser absorption of B from the nutrient solution and its greater total retention in the rootstock stem of plants grafted on Swingle citrumelo than those grafted on sour orange rootstock, thus limiting the amount of B that reached the leaves of plants grafted on Swingle citrumelo rootstock. Increased B concentration in the nutrient solution brought about a decrease of leaf thickness, mainly due to reduced spongy parenchyma tissue. Although the size of chloroplasts decreased in response to high B concentration in the nutrient solution, their shape was not altered. Excess B further decreased the relative volume of chloroplast thylakoids and increased the relative volume of plastoglobuli. Finally, the leaves of ‘Navelina’ plants grown under 0.25 mg B l−1 exhibited higher concentrations of chlorophyll as well as higher values of chlorophyll fluorescence parameters (Fv/Fm, Fv/F0) and of photosynthetic rates in contrast to the plants grown under 2.50 mg B l−1. [Copyright &y& Elsevier]