Leaf mechanisms for drought resistance in Zizyphus jujuba trees

No information exists on the mechanisms developed at the level of leaf water relations by pear-jujube trees (Zizyphus jujuba Mill.) to confront drought. For this reason, the purpose of the present study was to analyse its leaf water relations in order to clarify the resistance mechanisms (avoidance and tolerance) developed in response to a water stress and during recovery. Field-grown 7-year-old pear-jujube trees (cv. Grande de Albatera) were subjected to three irrigation treatments. Control (T0) plants were drip irrigated (112% ETo) in order to guarantee non-limiting soil water conditions, T1 plants (deficit irrigation, 64% ETo) were drip irrigated according to the criteria used by the grower and T2 plants irrigated as T0 but subjected to water withholding for 36 days and a subsequent re-irrigation at the levels used in T0 for 14 days, during the summer of 2011. The results indicated that pear-jujube plants confront water stress by developing stress avoidance and stress tolerance mechanisms. From the beginning of deficit irrigation (T1) and water withholding (T2) to when maximum water stress levels were achieved, leaf turgor was maintained allowing substantial gas exchange levels and, consequently, good leaf productivity. This leaf turgor maintenance was mainly due to two simultaneous and complementary mechanisms. Leaf conductance and the duration of maximum stomatal opening in water stressed plants decreased in order to control water loss via transpiration, contributing to maintain leaf turgor (stress avoidance mechanisms). Also, the gradual recovery of g(l) observed after rewatering the plants can be considered as a mechanism for promoting leaf rehydration. In addition, from the beginning of the stress period, active osmotic adjustment operated, also contributing to the maintenance of leaf turgor (stress tolerance mechanism). The high RWC(a) levels and the possibility of increasing the accumulation of water in the apoplasm in response to water stress, supporting a steeper gradient in water potential between the leaf and the soil, which can be considered another drought tolerance characteristic in pear-jujube.

Iron deficiency enhances bioactive phenolics in lemon juice

BACKGROUND

This study was designed to describe the phenolic status of lemon juice obtained from fruits of lemon trees differing in iron (Fe) nutritional status. Three types of Fe(III) compound were used in the experiment, namely a synthetic chelate and two complexes derived from natural polymers of humic and lignine nature.

RESULTS

All three Fe(III) compounds were able to improve the Fe nutritional status of lemon trees, though to different degrees. This Fe(III) compound effect led to changes in the polyphenol content of lemon juice. Total phenolics were decreased (∼33% average decrease) and, in particular, flavanones, flavones and flavonols were affected similarly.

CONCLUSION

Iron-deficient trees showed higher phenolic contents than Fe(III) compound-treated trees, though Fe deficiency had negative effects on the yield and visual quality of fruits. However, from a human nutritional point of view and owing to the health-beneficial properties of their bioavailable phenolic compounds, the nutritional quality of fruits of Fe-deficient lemon trees in terms of phenolics was higher than that of fruits of Fe(III) compound-treated lemon trees. Moreover, diosmetin-6,8-di-C-glucoside in lemon juice can be used as a marker for correction of Fe deficiency in lemon trees.