Aerial organs of plants being highly prone to local injuries, require tissue restoration to ensure their survival. However, knowledge of the underlying mechanism is sparse. In this study, we mimicked natural injuries in growing leaf and stem to study the reunion between mechanically disconnected tissues. We show that ()/ () genes, which encodes stem cell promoting factors, are activated and contribute to vascular regeneration in response to these injuries. PLT proteins bind to and activate the CUC2 promoter. Both PLT and CUC2 regulate the transcription of the local auxin biosynthesis gene YUC4 in a coherent feed forward loop, and this process is necessary to drive vascular regeneration. In the absence of this PLT mediated regeneration response, leaf ground tissue cells can neither acquire early vascular identity marker ATHB8, nor properly polarize auxin transporters to specify new venation paths. The PLT-CUC2 module is required for vascular regeneration, but is dispensable for midvein formation in leaf. We reveal the mechanisms of vascular regeneration in plants and distinguishes the wound repair ability of the tissue from its formation during normal development.

Pharmaceuticals remain in treated wastewater used to irrigate agricultural crops. Their effect on terrestrial plants is practically unknown. Here we tested whether these compounds can be considered as plant stress inducers. Several features characterize the general stress response in plants: production of reactive oxygen species acting as stress-response signals, MAPKs signaling cascade inducing expression of defense genes, heat shock proteins preventing protein denaturation and degradation, and amino acids playing signaling roles and involved in osmoregulation. Tomato seedlings bathing in a cocktail of pharmaceuticals (Carbamazepine, Valporic acid, Phenytoin, Diazepam, Lamotrigine) or in Carbamazepine alone, at different concentrations and during different time-periods, were used to study the patterns of stress-related markers. The accumulation of the stress-related biomarkers in leaf and root tissues pointed to a cumulative stress response, mobilizing the cell protection machinery to avoid metabolic modifications and to restore homeostasis. The described approach is suitable for the investigation of stress response of different crop plants to various contaminants present in treated wastewater.

Photosynthetic activity is affected by environmental factors and endogenous signals controlled by the source-sink relationship. We recently showed upregulated photosynthetic rate following partial defoliation under favorable environmental conditions. Here, we examined the influence of partial defoliation on the remaining leaves' function in tomato plants under nutrient deficiency. The effect of partial defoliation was more pronounced under limited mineral supply vs. favorable conditions. Reduced source-sink ratio resulted in increased stomatal conductance and transpiration rate, as well as higher photosystem II efficiency. Although chlorophyll concentration was significantly reduced under limited nutrient supply, the photosynthetic rate in the remaining leaf was similar to that measured under normal fertilization. Expression of genes involved in the phloem loading of assimilated sugars was downregulated in the remaining source leaf of unfertilized plants, 15 d after partial defoliation; in fertilized plants, these genes' expression was similar in control and partially defoliated plants. We propose that at early stage, the additional carbon assimilated in the remaining leaf is devoted to increasing source size rather than sink growth. The size increase of the remaining leaf in unfertilized plants was not sufficient to rebalance the source-sink ratio, resulting in inhibited sugar export and further carbohydrate allocation in the remaining leaf.

Photosynthetic activity is affected by exogenous and endogenous inputs, including source-sink balance. Reducing the source to sink ratio by partial defoliation or heavy shading resulted in significant elevation of the photosynthetic rate in the remaining leaf of tomato plants within 3 d. The remaining leaf turned deep green, and its area increased by almost 3-fold within 7 d. Analyses of photosynthetic activity established up-regulation due to increased carbon fixation activity in the remaining leaf, rather than due to altered water balance. Moreover, senescence of the remaining leaf was significantly inhibited. As expected, carbohydrate concentration was lower in the remaining leaf than in the control leaves; however, expression of genes involved in sucrose export was significantly lower. These results suggest that the accumulated fixed carbohydrates were primarily devoted to increasing the size of the remaining leaf. Detailed analyses of the cytokinin content indicated that partial defoliation alters cytokinin biosynthesis in the roots, resulting in a higher concentration of trans-zeatin riboside, the major xylem-translocated molecule, and a higher concentration of total cytokinin in the remaining leaf. Together, our findings suggest that trans-zeatin riboside acts as a signal molecule that traffics from the root to the remaining leaf to alter gene expression and elevate photosynthetic activity. © The Author(s) 2019. Published by Oxford University Press on behalf of the Society for Experimental Biology.

The interactions between temperature, relative humidity, radiation, wind speed and their effect on plant transpiration in the context of water consumption for irrigation purposes have been studied for over a century. Leaf area has also been established as an important factor affecting water consumption. We analyzed a multivariable time series composed of both meteorological and vegetative variables with a daily temporal resolution for the growing seasons of 2013–2016 for Vitis vinfera ‘Cabernet Sauvignon’ vineyards in the mountainous region in Israel. Time-series analysis of this data was used to characterize seasonal patterns affecting water consumption (ETc) of vines and to quantify interrelations between meteorological and vegetative factors affecting vine water consumption. Moreover, we applied a machine learning regression model to determine the relative influence of meteorological and vegetative factors on ETc during four growing seasons. Finally, we developed an ensemble model for temporally forecasting vine ETc for an additional season using a training dataset of multiple variables. Our findings show that decomposing the time-series dataset uncovered a wider variety of underlying temporal patterns, and enabled quantification of seasonal and daily relationships. Leaf area had a substantial impact on ETc and was found to have a relative influence ranging between 62 and 86% for the different growing seasons. Mean temperature was ranked second followed by minor effects of relative humidity, solar radiation and wind speed that were interchangeably ordered. The ensemble model produced reliable results, with cross validation coefficients   0.9. Incorporating leaf area measurements into the regression model improved both the performance of the model and the training data correlation. Using time-series statistics to explore meteorological and vegetative temporal characteristics, patterns, interrelations and relative effect on evapotranspiration may facilitate the understanding of water consumption processes and assist in generating more effective and skillful irrigation models. © 2019 Elsevier B.V.