Water infiltration experiments indicate that cv. Müller-Thurgau and several Vitis spp. belong to the heterobaric leaf type which is characterised by airtight intercellular chambers in the mesophyll. Stomatal closure of heterobaric leaves was non-uniform if leaves were exposed to low air humidity.
Leaf conductance was correlated with the infiltrated leaf area and the amount of infiltrated water. Taking into account non-uniform stomatal closure of vine leaves in the calculation of intercellular CO2 partial pressure (pi) (DOWNTON et al. 1988 b), piwas reduced at low air humidity. The almost identical carboxylation efficiency (A/pi) under moist and dry air conditions indicates that the decline of the photosynthetic rate caused by dry air is entirely due to stomatal limitation of CO2 uptake.
Niedrige Luftfeuchte verursacht uneinheitlichen Stomataschluß bei heteroharischen Blättern von Vitis-Arten
Mit Hilfe der Infiltrationsmethode wurde bei Müller-Thurgau sowie verschiedenen Vitis-Arten gezeigt, daß Reben einen heterobarischen Blattypus besitzen, bei dem das Mesophyll in luftdichte, kammerartige Interzellularsysteme unterteilt ist. Der Stomataschluß dieser heterobarischen Blätter war uneinheitlich, wenn die Blätter einer niedrigen Luftfeuchte ausgesetzt wurden. Die Blattleitfähigkeit korrelierte mit dem Anteil der infiltrierten Blattfläche bzw. mit der infiltrierten Wassermenge. Wurde die Uneinheitlichkeit des Stomataschlusses in trockener Luft bei der Berechnung des interzellulären CO2-Partialdruckes (pi) berücksichtigt (vgl. DoWNTON et al. 1988 b), ergab sich eine Abnahme von pi· Die nahezu gleiche Carboxylierungseffizienz bei hoher und geringer Luftfeuchte verdeutlicht, daß die Abnahme der Photosyntheseleistlung bei geringer Luftfeuchte ausschließlich über eine stomatär bedingte Verminderung der CO2-Aufnahme zu erklären ist.
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The relationship between nitric oxide (NO) reduction and the inhibition of abscisic acid (ABA)-induced stomatal closure by ethylene was analysed. ABA treatment induced NO production and stomatal closure, but ethylene inhibited the effects of ABA on these two parameters.
Like 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (cPTIO), a specific scavenger of NO, haemoglobin (Hb), the potent scavenger of NO/carbon monoxide (CO) and N-nitro-L-Arg-methyl ester (L-NAME), an inhibitor of animal nitric oxide synthases (NOS; EC 18.104.22.168), both the ethylene-releasing compound 2-chloroethylene phosphonic acid (ethephon, ETH) and 1-aminocyclopropane-1-carboxylic acid (ACC), the immediate precursor of ethylene, were found to inhibit stomatal closure by ABA and to reduce NO levels by ABA in guard cells, indicating that the ethylene-caused inhibition of ABA-induced stomatal closure involves a decrease in NO levels in guard cells.
In addition, and similar to cPTIO and Hb, ACC/ETH suppressed sodium nitroprusside (SNP)-induced stomatal closure and NO levels in guard cells treated with SNP in the light. ACC/ETH also reopened stomata that had been closed by ABA and reduced NO levels that had been generated by ABA, showing that ethylene causes NO removal in guard cells.
However, the above-mentioned effect of ACC/ETH was dissimilar to that of L-NAME, which was incapable of reducing NO levels by SNP or abolishing NO that had been generated by ABA.
We suggest that ethylene probably induces NO removal, thereby reducing NO levels in Vicia faba guard cells, and finally inhibits stomatal closure induced by ABA.
Furthermore, the pattern of NO reduction caused by ethylene is also discussed.
The epidermal cells of the juvenile leaves of maize are covered by a wax layer. glossy mutants are known which reduce drastically wax deposition. We have used the somatically unstable glossy-1 mutable 8 allele to study the distribution on the epidermis of spontaneous revertant sectors of wild- type tissues.
Sectors tend to start and end at positions that correlate with the location on the epidermis of the long costal cells of ribs.
It is concluded that in the protoderm only a few cells have a role and position in the generation of each of the developmental modules located between leaf midrib and margin. The module consists of an epidermal strip of cells bordered by two lateral ribs. The module originates from at least 4 cells, with one cel l being the progenitor of the other three. Data are provided describing the mode of longitudinal anticlinal epidermal cell divisions within the module that are responsible for the increase in leaf width.
The results suggest the existence of a clonal type of development during early leaf epidermis formation.
Drought is one of the abiotic stresses which impairs the plant growth/development and restricts the yield of many crops throughout the world.
Stomatal closure is a common adaptation response of plants to the onset of drought condition. Stomata are microscopic pores on the leaf epidermis, which regulate the transpiration/CO2 uptake by leaves. Stomatal guard cells can sense various abiotic and biotic stress stimuli from the internal and external environment and respond quickly to initiate closure under unfavorable conditions.
Stomata also limit the entry of pathogens into leaves, restricting their invasion. Drought is accompanied by the production and/or mobilization of the phytohormone, abscisic acid (ABA), which is well-known for its ability to induce stomatal closure. Apart from the ABA, various other factors that accumulate during drought and affect the stomatal function are plant hormones (auxins, MJ, ethylene, brassinosteroids, and cytokinins), microbial elicitors (salicylic acid, harpin, Flg 22, and chitosan), and polyamines .
The role of various signaling components/secondary messengers during stomatal opening or closure has been a matter of intense investigation. Reactive oxygen species (ROS), nitric oxide (NO), cytosolic pH, and calcium are some of the well-documented signaling components during stomatal closure.
The interrelationship and interactions of these signaling components such as ROS, NO, cytosolic pH, and free Ca²⁺ are quite complex and need further detailed examination.
Improvement of crop drought resistance and water use efficiency (WUE) has been a major endeavor in agriculture. Arabidopsis ENHANCED DROUGHT TOLERANCE1/HOMEODOMAIN GLABROUS11 (AtEDT1/HDG11), a homeodomain‐START transcription factor we previously identified from enhanced drought tolerance1 mutant (edt1), has been demonstrated to significantly improve drought tolerance and WUE in multiple plant species when constitutively overexpressed.
Here, we report the genetic evidence suggesting a genetic pathway, which consists of EDT1/HDG11, ERECTA, and E2Fa loci, and regulates WUE by modulating stomatal density. AtEDT1/HDG11 transcriptionally activates ERECTA by binding to HD cis‐elements in the ERECTA promoter. ERECTA in turn depends on E2Fa to modulate the expression of cell cycle‐related genes.
This modulation affects the transition from mitosis to endocycle, leading to increased ploidy levels in leaf cells, and therefore increased cell size and decreased stomatal density.
Our results suggest a possible EDT1/HDG11‐ERECTA‐E2Fa genetic pathway that reduces stomatal density by increasing cell size and provide a new avenue to improve WUE of crops.
Immunity at cauliflower hydathodes controls systemic infection by Xanthomonas campestris pv campestris
by Cerutti A., Jauneau A., Auriac M.-C., Lauber E., Martinez Y., Chiarenza S., Leonhardt N., Berthomé R., Noël L. D. (2017)
1, 2, 3 : Cerutti A., Jauneau A., Auriac M.-C., Lauber E., Martinez Y., Chiarenza S., Leonhardt N., Berthomé R.,
4, 5, 6 Noël L. D.
1 LIPM, Université de Toulouse, INRA, CNRS, UPS, F-31326 Castanet-Tolosan, France (A.C., E.L., R.B., L.D.N.).
2 Institut Fédératif de Recherche 3450, Plateforme Imagerie, Pôle de Biotechnologie Végétale, F-31326 Castanet-Tolosan, France (A.J., M.-C.A., Y.M.); and.
3 UMR7265, Laboratoire de Biologie du Développement des Plantes, Service de Biologie Végétale et de Microbiologie Environnementales, Institut de Biologie Environnementale et Biotechnologie, Centre National de la Recherche Scientifique-Commissariat à l’Energie Atomique-Université Aix-Marseille, F-13108 Saint Paul-Les-Durance, France (S.C., N.L.).
4 LIPM, Université de Toulouse, INRA, CNRS, UPS, F-31326 Castanet-Tolosan, France (A.C., E.L., R.B., L.D.N.)
5 Institut Fédératif de Recherche 3450, Plateforme Imagerie, Pôle de Biotechnologie Végétale, F-31326 Castanet-Tolosan, France (A.J., M.-C.A., Y.M.);
6 UMR7265, Laboratoire de Biologie du Développement des Plantes, Service de Biologie Végétale et de Microbiologie Environnementales, Institut de Biologie Environnementale et Biotechnologie, Centre National de la Recherche Scientifique-Commissariat à l’Energie Atomique-Université Aix-Marseille, F-13108 Saint Paul-Les-Durance, France (S.C., N.L.) .
In Plant Physiol 174: 700–716 – doi: 10.1104/pp.16.01852. –
Hydathodes are water pores found on leaves of a wide range of vascular plants and are the sites of guttation.
We report here on the detailed anatomy of cauliflower (Brassicaoleracea) and Arabidopsis (Arabidopsis thaliana) hydathodes. Hydathode surface presents pores resembling stomata giving access to large cavities. Beneath, the epithem is composed of a lacunar and highly vascularized parenchyma offering a direct connection between leaf surface and xylem vessels.
Arabidopsis hydathode pores were responsive to ABA and light similar to stomata. The flg22 flagellin peptide, a well-characterized elicitor of plant basal immunity, did not induce closure of hydathode pores in contrast to stomata. Because hydathodes are natural infection routes for several pathogens, we investigated hydathode infection by the adapted vascular phytopathogenic bacterium Xanthomonas campestris pv campestris (Xcc), the causal agent of black rot disease of Brassicaceae. Microscopic observations of hydathodes six days postinoculation indicated a digestion of the epithem cells and a high bacterial multiplication. Postinvasive immunity was shown to limit pathogen growth in the epithem and is actively suppressed by the type III secretion system and its effector proteins. Altogether, these results give a detailed anatomic description of Brassicaceae hydathodes and highlight the efficient use of this tissue as an initial niche for subsequent vascular systemic dissemination of Xcc in distant plant tissues.