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Proposed mechanisms of embolism recovery are controversial for plants that are transpiring while undergoing cycles of dehydration and rehydration. Here, water stress was imposed on grapevines (Vitis vinifera), and the course of embolism recovery, leaf water potential (Ψleaf), transpiration (E) and abscisic acid (ABA) concentration followed during the rehydration process. As expected, Ψleaf and E decreased upon water stress, whereas xylem embolism and leaf ABA concentration increased. Upon rehydration, Ψleaf recovered in 5 h, whereas E fully recovered only after an additional 48 h. The ABA content of recovering leaves was higher than in droughted controls, both on the day of rewatering and the day after, suggesting that ABA accumulated in roots during drought was delivered to the rehydrated leaves. In recovering plants, xylem embolism in petioles, shoots, and roots decreased during the 24 h following rehydration. A model is proposed to describe plant recovery after rehydration based on three main points: embolism repair occurs progressively in shoots and further in roots and in petioles, following an almost full recovery of Ψleaf; hydraulic conductance recovers during diurnal transpiring hours, when formation and repair of embolisms occurs in all plant organs; an ABA residual signal in rehydrated leaves hinders stomatal opening even when water relations have recovered, suggesting that an ABA-induced transpiration control promotes gradual embolism repair in rehydrated grapevines.

Tomato plants harboring the ripening-inhibitor (rin) mutation yield fruits that fail to ripen. Additionally, rin plants display enlarged sepals and loss of inflorescence determinacy. Positional cloning of the rin locus revealed two tandem MADS-box genes (LeMADS-RIN and LeMADS-MC), whose expression patterns suggested roles in fruit ripening and sepal development, respectively. The rin mutation alters expression of both genes. Gene repression and mutant complementation demonstrate that LeMADS-RIN regulates ripening, whereas LeMADS-MC affects sepal development and inflorescence determinacy. LeMADS-RIN demonstrates an agriculturally important function of plant MADS-box genes and provides molecular insight into nonhormonal (developmental) regulation of ripening.

The objectives of the study were to identify the relevant hydraulic parameters associated with stomatal regulation during water stress and to test the hypothesis of a stomatal control of xylem embolism in walnut (Juglans regia × nigra) trees. The hydraulic characteristics of the sap pathway were experimentally altered with different methods to alter plant transpiration ($E_{\\text{plant}}$) and stomatal conductance (gs). Potted trees were exposed to a soil water depletion to alter soil water potential ($\\Psi _{\\text{soil}}$), soil resistance ($R_{\\text{soil}}$), and root hydraulic resistances ($R_{\\text{root}}$). Soil temperature was changed to alter $R_{\\text{root}}$ alone. Embolism was created in the trunk to increase shoot resistance ($R_{\\text{shoot}}$). Stomata closed in response to these stresses with the effect of maintaining the water pressure in the leaf rachis xylem ($P_{\\text{rachis}}$) above -1.4 MPa and the leaf water potential ($\\Psi _{\\text{leaf}}$) above -1.6 MPa. The same dependence of $E_{\\text{plant}}$ and gs on $P_{\\text{rachis}}$ or $\\Psi _{\\text{leaf}}$ was always observed. This suggested that stomata were not responding to changes in $\\Psi _{\\text{soil}}$, $R_{\\text{soil}}$, $R_{\\text{root}}$, or $R_{\\text{shoot}}$ per se but rather to their impact on $P_{\\text{rachis}}$ and/or $\\Psi _{\\text{leaf}}$. Leaf rachis was the most vulnerable organ, with a threshold $P_{\\text{rachis}}$ for embolism induction of -1.4 MPa. The minimum $\\Psi _{\\text{leaf}}$ values corresponded to leaf turgor loss point. This suggested that stomata are responding to leaf water status as determined by transpiration rate and plant hydraulics and that $P_{\\text{rachis}}$ might be the physiological parameter regulated by stomatal closure during water stress, which would have the effect of preventing extensive developments of cavitation during water stress.

The average first flowering date of 385 British plant species has advanced by 4.5 days during the past decade compared with the previous four decades: 16% of species flowered significantly earlier in the 1990s than previously, with an average advancement of 15 days in a decade. Ten species (3%) flowered significantly later in the 1990s than previously. These data reveal the strongest biological signal yet of climatic change. Flowering is especially sensitive to the temperature in the previous month, and spring-flowering species are most responsive. However, large interspecific differences in this response will affect both the structure of plant communities and gene flow between species as climate warms. Annuals are more likely to flower early than congeneric perennials, and insect-pollinated species more than wind-pollinated ones.

Multiple environmental and endogenous inputs regulate when plants flower. The molecular genetic dissection of flowering time control in Arabidopsis has identified an integrated network of pathways that quantitatively control the timing of this developmental switch. This framework provides the basis to understand the evolution of different reproductive strategies and how floral pathways interact through seasonal progression.

Nitric oxide (NO) is a very active molecule involved in many and diverse biological pathways where it has proved to be protective against damages provoked by oxidative stress conditions. In this work, we studied the effect of two NO donors, sodium nitroprusside (SNP) and S-nitroso-N-acetylpenicillamine SNP-treated on the response of wheat (Triticum aestivum) to water stress conditions. After 2 and 3 h of drought, detached wheat leaves pretreated with 150 μM SNP retained up to 15% more water than those pretreated with water or $\\text{NO}_{2}{}^{-}/\\text{NO}_{3}{}^{-}$. The effect of SNP treatment on water retention was also found in wheat seedlings after 7 d of drought. These results were consistent with a 20% decrease in the transpiration rate of SNP-treated detached wheat leaves for the same analyzed time. In parallel experiments, NO was also able to induce a 35%, 30%, and 65% of stomatal closure in three different species, Tradescantia sp. (monocotyledonous) and two dicotyledonous, Salpichroa organifolia and fava bean (Vicia faba), respectively. In SNP-treated leaves of Tradescantia sp., the stomatal closure was correlated with a 10% increase on RWC. Ion leakage, a cell injury index, was 25% lower in SNP-treated wheat leaves compared with control ones after the recovery period. Carboxy-PTIO (2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide), a specific NO scavenger, reverted SNP action by restoring the transpiration rate, stomatal aperture, and the ion leakage to the level found in untreated leaves. Northern-blot analysis showed that SNP-treated wheat leaves display a 2-fold accumulation of a group three late embryogenesis abundant transcript with respect to control leaves both after 2 and 4 h of drought periods. All together, these results suggest that the exogenous application of NO donors might confer an increased tolerance to severe drought stress conditions in plants.

Flowering is often triggered by exposing plants to appropriate day lengths. This response requires an endogenous timer called the circadian clock to measure the duration of the day or night 1 . This timer also controls daily rhythms in gene expression and behavioural patterns such as leaf movements. Several Arabidopsis mutations affect both circadian processes and flowering time 2 , 3 , 4 , 5 , 6 , 7 , 8 , 9 , 10 ; but how the effect of these mutations on the circadian clock is related to their influence on flowering remains unknown. Here we show that expression of CONSTANS ( CO ), a gene that accelerates flowering in response to long days 11 , is modulated by the circadian clock and day length. Expression of a CO target gene, called FLOWERING LOCUS T ( FT ), is restricted to a similar time of day as expression of CO . Three mutations that affect circadian rhythms and flowering time alter CO and FT expression in ways that are consistent with their effects on flowering. In addition, the late flowering phenotype of such mutants is corrected by overexpressing CO . Thus, CO acts between the circadian clock and the control of flowering, suggesting mechanisms by which day length regulates flowering time.

• Background and aims Much recent study of plant trichomes has focused on various aspects of glandular secreting trichomes (GSTs) and differentiation of simple trichomes. This Botanical Briefing will highlight: ‐ research on various aspects of, and manipulation of glandular secreting trichomes; ‐ molecular aspects of the differentiation and development of simple trichomes of arabidopsis and cotton; ‐ how methods for manipulation of model systems used in the above work can be applied to expand our understanding of less studied surface structures of plants. • Scope The Briefing will cover: ‐ established and suggested roles of simple and glandular secreting trichomes; ‐ recent results regarding solute and ion movement in trichomes; ‐ methods for isolating trichomes; ‐ recent studies of trichome differentiation and development; ‐ attempts to modify metabolism in secreting trichomes; ‐ efforts to exploit trichomes for commercial and agronomic purposes.

We review the photosynthetic responses to drought in field-grown grapevines and other species. As in other plant species, the relationship between photosynthesis and leaf water potential and/or relative water content in field-grown grapevines depends on conditions during plant growth and measurements. However, when light-saturated stomatal conductance was used as the reference parameter to reflect drought intensity, a common response pattern was observed that was much less dependent on the species and conditions. Many photosynthetic parameters (e.g. electron transport rate, carboxylation efficiency, intrinsic water-use efficiency, respiration rate in the light, etc.) were also more strongly correlated with stomatal conductance than with water status itself. Moreover, steady-state chlorophyll fluorescence also showed a high dependency on stomatal conductance. This is discussed in terms of an integrated down-regulation of the whole photosynthetic process by CO2 availability in the mesophyll. A study with six Mediterranean shrubs revealed that, in spite of some marked interspecific differences, all followed the same pattern of dependence of photosynthetic processes on stomatal conductance, and this pattern was quite similar to that of grapevines. Further analysis of the available literature suggests that the above-mentioned pattern is general for C3 plants. Even though the patterns described do not necessarily imply a cause and effect relationship, they can help our understanding of the apparent contradictions concerning stomatal vs. non-stomatal limitations to photosynthesis under drought. The significance of these findings for the improvement of water-use efficiency of crops is discussed.

In plants, numerous Ca2+-stimulated protein kinase activities occur through calcium-dependent protein kinases (CDPKs). These novel calcium sensors are likely to be crucial mediators of responses to diverse endogenous and environmental cues. However, the precise biological function(s) of most CDPKs remains elusive. The Arabidopsis genome is predicted to encode 34 different CDPKs. In this Update, we analyze the Arabidopsis CDPK gene family and review the expression, regulation, and possible functions of plant CDPKs. By combining emerging cellular and genomic technologies with genetic and biochemical approaches, the characterization of Arabidopsis CDPKs provides a valuable opportunity to understand the plant calcium-signaling network.