Abnormal Stomatal Behaviour and Leaf Anatomy in Capsicum annuum, scabrous diminutive, a Wilty Mutant of Pepper

An attempt is made to explain the tendency to excessive wiltingin scabrous diminutive, a pepper mutant. For this, mutant andnormal plants were compared with respect to leaf anatomy, transpirationof whole plants and detached drying leaves, density and openingof stomata, staining of potassium in epidermal cells and rootpressure. A much greater proportion of intracellular space was found inthe mutant leaf which contains fewer and smaller mesophyll cellsthan the normal plant. The anticlinal walls of the epidermisof the mutant leaf were almost straight whereas those of thenormal were wavy. Transpiration per unit leaf area of wholeplants, percentage of stomata open both day and night, and waterloss from detached drying leaves were all higher in the mutant.Potassium staining in guard cells was similar in both planttypes, slightly less in darkness and marginally higher in light.The subsidiary cells of normal leaves did not stain at all,but those of the mutant leaves stained heavily in both lightand darkness. Root pressure was lower in the mutant. Possible explanations for the tendency of the pepper mutantto wilt are discussed.     

Ion Imbalance in Capsicum annuum, scabrous diminutive, a Wilty Mutant of Pepper I. SODIUM FLUXES

Leaves of the wilty pepper mutant, scabrous diminutive, accumulatemore Na+ than those of the normal genotype, when both grow inmedium containing N⁺. It seems that the regulation of Na⁺ fluxin the mutant root was modified. Net uptake of Na⁺ was muchhigher and efflux of ²²Na⁺ was lower in the mutant roots thanin the normal ones. Two possible explanations for these differencesbetween mutant and normal plants are discussed, namely (a) achange in membrane permeability and (b) a change in the mechanismof Na⁺ extrusion.     

Ion Imbalance in Capsicum annum scarbrous diminutive a Wilty Mutant of pepper: II.RUBIDIUM FLUX

Root tips of the wilty pepper mutant scarbrous diminutive accumulateless rubidium than those of the normal genotype. This phenomenonwas evident in root tips excised from plants maintained for2 d in CaSO₄ solution (low salt plants), especially in the lowerexternal concentration range (0.1– 1.0 mM) of RbCl. Theefflux rate of Rb⁺ from mutant root tips was twice as high asin normal root tips. These results indicate that the ability of the mutant rootsto absorb and accumulate Rb⁺ and K⁺ is impaired. This defectcould be a consequence of either an impaired Na⁺/K⁺ carriersystem, or increased leakiness of mutant membranes, or both. The fact that the normal roots can accumulate Rb⁺ much fasterthan mutant roots supports the first alternative, i.e. thatthe high affinity carrier system was impaired in the mutantroots. However, the higher efflux rate of Rb⁺ from the mutantroots suggests that membrane leakiness was also affected.     

Abnormal Stomatal Behaviour and Hormonal Imbalance in flacca, a Wilty Mutant of Tomato: EFFECT OF ABSCISIC ACID AND AUXIN ON STOMATAL BEHAVIOUR AND PEROXIDASE ACTIVITY

The wilty tomato mutant flacca and the normal variety RheinlandsRuhm were compared in terms of: (1) potassium transport intoand out of the guard cells, (2) cell wall properties which includeprotein, hydroxyproline and peroxidase activity, and (3) activityof indol-3yl-acetic acid oxidase. Also studied were the effectsof auxin on stomatal behaviour and peroxidase activity whenapplied to normal plants during development, and the short-termeffect of abscisic acid on the resistance of flacca stomatato closure under plasmolysis. Potassium transport, wall protein and hydroxyproline all seemedto be equal in mutant and normal plants. Peroxidase activitywas higher in the soluble and wall fractions of the mutant,and decreased toward normal in the mutant treated with abscisicacid. More stomata were open and peroxidase activity was higherin normal plants treated with auxin during development. Thepercentage of open stomata under plasmolysis was lower and theiraperture size was smaller in the epidermal strips taken fromabscisic-acid-treated mutant plants than from control mutantplants.     

Abnormal Stomatal Behavior and Hormonal Imbalance in flacca, a Wilty Mutant of Tomato: II. Auxin- and Abscisic Acid-like Activity

The wilty tomato mutant, flacca, and the control variety, Rheinlands Ruhm, were compared with regard to the endogenous activity and concentration of auxin- and abscisic acid-like substances during ontogeny. The mutant wilts fast under water deficit because of inability to close its stomata. Symptoms characteristic of excessive auxin are evident in the developing mutant. Among these symptoms are branch and leaf epinasty, excessive rooting along the stem, and increased apical dominance. By using a leucine-incorporation assay, spray of whole plants with 2,4-dichlorophenoxyacetic acid, and wheat coleoptile bioassay, indications were found of an excess of activity and concentration of auxin-like substances in shoots of young and mature mutant plants. The wheat coleoptile bioassay also revealed a much lower amount of substances with abscisic acid-like activity in the mutant compared with the normal plant. In contrast to the appearance during ontogeny of morphological symptoms characteristic of auxin excess in the mutant, the absolute amount of auxin-like substances and their activity in incorporation of leucine decreased with age. A parallel decrease of the concentration and activity of auxin-like compounds was also found in the normal plant. The concentration of abscisic acid-like substances increased with age in both genotypes. The disagreement between the increasing morphological symptoms and the decrease of auxin-like activity and concentration is discussed, together with the possibility of a causal relationship between auxin-and abscisic acid-like activity and stomatal behavior.     

Abnormal Stomatal Behavior and Hormonal Imbalance in flacca, a Wilty Mutant of Tomato: I. Root Effect and Kinetin-like Activity

The wilty tomato mutant, flacca, and the normal variety, Rheinlands Ruhm, were compared for kinetin-like activity in ontogeny. The mutant wilts easily because its stomata resist closure. This stomatal resistance decreases with age. The occurrence of a root factor which induces stomatal opening was inferred from grafting experiments. It was hypothesized that the excessive stomatal openings in the mutant may result from excess of kinetin-like activity in the leaf of that plant. In addition, it was suggested that the closure of stomata in the aging mutant is due to a decrease of kinetin-like activity with age. Kinetin-like activity in the leaf was determined by incorporation of labeled leucine. The concentration of cytokinins in root exudate and leaf extract was determined by the soybean callus assay. Evidence was presented of higher kinetin-like activity in the leaves of the mutant and higher cytokinin concentration in its root exudate. Cytokinin concentration in the shoot was found to be only slightly higher in the mutant than in the normal plants. Kinetin-like activity in the leaf and cytokinin concentration of root exudate decreased with age in both mutant and normal plants. Kinetin-like activity in the leaves of mutant plants, which phenocopy the normal variety as a result of continuous application of abscisic acid, was lower than in control mutant plants. The significance of these findings per se and in connection with stomatal behavior is discussed.     

Control of Ion Fluxes in Stomatal Guard Cells

Opening and closing of the stomatal pore is associated with very large changes in K-salt accumulation in stomatal guard cells. This review discusses the ionic relations of guard cells in relation to the general pattern of transport processes in plant cells, in plasmalemma and tonoplast, involving primary active transport of protons, proton-linked secondary active transport, and a number of gated ion channels. The evidence available suggests that the initiation of stomatal opening is regulated through the uptake mechanisms, whereas initiation of stomatal closing is regulated by control of ion efflux at the plasmalemma, and of fluxes to and from the vacuole. In response to a closing signal there are large transient increases in efflux of both Cl^? (or Br^?) and Rb⁺ (K⁺) at the plasmalemma, with also a probable increase in anion flux from vacuole to cytoplasm and decrease in anion flux from cytoplasm to vacuole. A speculative hypothetical sequence of events is discussed, by which the primary response to a closing signal is an increase in Ca²⁺ influx at the plasmalemma, producing depolarisation and increase in cytoplasmic Ca²⁺. The consequent opening of Ca²⁺-sensitive Cl^? channels, and voltage-sensitive K⁺ channels (also Ca²⁺-sensitive?) in the plasmalemma, and of a Ca²⁺-sensitive nonspecific channel in the tonoplast, could produce the flux effects identified by the tracer work; this speculation is also consistent with the Ca²⁺-sensitivity of the response to closing signals and with evidence from patch clamping that such channels exist in at least some plant cells, though not yet all shown in guard cells.     

Abnormal Stomatal Behavior and Hormonal Imbalance in flacca, a Wilty Mutant of Tomato: V. Effect of Abscisic Acid on Indoleacetic Acid Metabolism and Ethylene Evolution

The wilty tomato mutant flacca, the normal cultivar Lycopersicon esculentum Mill. Rheinlands Ruhm, and abscisic acid-induced phenotypic revertants were compared with respect to ethylene evolution, activity of tryptophan aminotransferase, and [1-¹⁴C]indoleacetic acid decarboxylation.     

Abnormal Stomatal Behavior and Hormonal Imbalance in flacca, a Wilty Mutant of Tomato: IV. Effect of Abscisic Acid and Water Content on RNase Activity and RNA

Plants of the wilty tomato (Lycopersicum esculentum) mutant, flacca, and of the normal cultivar Rheinlands Ruhm growing under either “normal” or high humidity were used in this research. Under normal humidity, RNase activity was much higher in mutant plants in which abscisic acid (ABA) and water content were lower than in the normal plant. The mutant also contained less RNA and protein per cell and less soluble RNA relative to ribosomal RNA as compared with the normal genotype. In ABA-treated mutant plants, RNase activity decreased while RNA, protein, the ratio of soluble to ribosomal RNA and water content increased.     

Studies in Stomatal Behaviour: IV. THE WATER-RELATIONS OF THE EPIDERMIS

1. It is shown that a dry external atmosphere exerts the followingeffects on stomatal movement:

1. A striking accelaration ofclosure in darkness.
2. A slight acceleration of opening in light.
3. If the water-supply to the leaf is impaired, an inabilitytomaintain full opening in the light.

Conversely, a saturatedexternal atmosphere induces sluggishness of movement and a tendencyto incomplete closure in darkness.

1. These results are consideredto support La Rue's contentionthat the epidermal water-supplyis drawn solely by lateral movementfrom the main veins, andnot from the underlying mesophyll.The stomatal phenomena themselvesdo not appear capable of anysimple explanation based on currentknowledge of guard-cellphysiology.
2. The biological significanceof these results is discussed, withparticular reference tothe problem of xeromorphic structures,for which a new interpretationis suggested.

     

The Effects of Cytokinins and ABA on Stomatal Behaviour of Maize and Commelina

Epidermal strips and leaf fragments of Commelina and leaf fragmentsof maize were incubated on solutions containing naturally-occurringor synthetic cytokinins and/or ABA. The effects of these treatmentson stomatal behaviour were assessed. Cytokinins alone did notpromote stomatal opening in either species but concentrationsof both zeatin and kinetin from 10^–3 to 10^–1 molm^–3 caused some reversal of ABA-stimulated closure ofmaize stomata. The reversal of the ABA effect increased withincreasing cytokinin concentration. Cytokinins had no effecton ABA-stimulated closure of Commelina stomata. When appliedalone, at high concentration (10^–1 mol m^–3), toCommelina epidermis or leaf pieces both zeatin and kinetin restrictedstomatal opening. Key words: ABA, Cytokinins, Stomata, Maize, Commelina     

Control of Stomatal Behaviour by Abscisic Acid which Apparently Originates in the Roots

Two experiments indicate that abscisic acid (ABA) may influencestomatal behaviour of Commelina communis L. Stomatal conductancecould not be correlated with bulk leaf ABA content but whenthe abaxial epidermis was assayed for ABA, small increases inABA content correlated well with limitations of leaf conductance.Restricted conductance of the abaxial surface of leaves wasassociated with an increase of approximately 40 amole ABA perstomatal complex. This agrees with previously published figures. When roots of individual plants were split between two containers,drying the soil around one part of the root system restrictedleaf conductance, even though leaf water relations were notaffected. Increased ABA content of the epidermis coincided withincreased ABA content of the roots in drying soil. Other rootsof the same plant in moist soil did not show increased ABA content.These results suggest that in drying soil, ABA can move fromthe roots to the epidermis and restrict stomatal aperture evenwhen leaf water potentials and turgors remain constant. Theimportance of this mechanism in providing a sensitive foliarresponse to decreasing soil moisture is discussed. Key words: Soil drying, ABA, roots, stomata, water relations     

Studies in Stomatal Behaviour: XII. OPENING IN HIGH TEMPERATURE IN DARKNESS

Xanthium pennsylvanicum exhibited a small stomatal opening (‘nightopening’) towards the end of a long night at 27? C. Experimentsare described in which a temperature increase from 27? to 36?,given during the period of night opening, caused the stomatato open widely for several hours. The degree of opening firstachieved was comparable with that observed in light of 1,000lux, but high temperature was less efficient than light formaintaining opening. Openmg was greater in mature than in youngleaves. The opening did not appear to be due to water strainunder the high temperature. It was found that temperature-induced opening was much greaterafter a long night (16 hours) than after a short night (fourhours). From this it is deduced that the opening is affectedby the endogenous rhythm which occurs in darkness (this wasstudied in previous work). The results obtained here contrastsharply with some obtained previously (and confirmed here) inwhich different temperatures were given throughout the night.The differences can probably be explained in terms of temperatureeffects on the endogenous rhythm. The stomata retained their normal responses to carbon dioxideand carbon dioxide-free air during temperature-induced opening.Thus the opening must occur in spite of any temperature stimulationof respiration. An experiment on the effect of temperature on stomatal closurein response to darkness is also described. Closure was significantlyslower at 36? than at 27? C.     

Arabic morphology: diminutive verbs and diminutive nouns in San’ani Arabic

Word formation in Arabic has traditionally been assumed to involve interdigitation of a consonantal root with a vocalic pattern. This view is adopted by a large number of modern generative morphologists. More recently, however, several morphologists have argued that words in Semitic are formed from fully vocalised stems. In this paper, I argue that in San'ani (the dialect of San'a), and in some other Arabic dialects, there is a class of verbs that have as part of either their denotations or connotations a diminutive sense. I then consider diminutive nouns in the dialect. On the basis of semantic and phonological relationships between diminutive verbs and their non-diminutive counterparts, as well as native speakers' explanations of certain diminutive verbs, and the relationship between diminutive nouns and their non-diminutive counterparts, I argue that while some derivational processes take the root as the basic morphological unit, phonological and semantic similarities between certain stems can only be accounted for by derivation from a fully vocalised stem. I therefore conclude that both root-based and stem-based types of word formation occur.     

植物保卫细胞离子通道在气孔运动中的作用

介绍保卫细胞质膜和液泡膜上的离子通道活性变化及其在气孔运动中的作用,同时对各种刺激引发气孔运动过程中的信使Ca2 、H2O2和pH等对离子通道的调节作用作了概述.     

Abnormal Stomatal Opening in Coconut Palms Affected with Root (Wilt) Disease

Studies on the stomatal regulation in the root (wilt) affectedcoconut palms (Cocos nucifera L.) revealed that the diseasedpalms had low stomatal resistance compared to the healthy palms,irrespective of their age. The same trend was observed whetherthe determinations were made at different times of the day (6–18h) or under irrigated and unirrigated conditions or in differentseasons (‘dry’ and ‘wet’). Thus, thestomatal regulation was significantly impaired in the diseasedpalms resulting in excessive water loss compared to the healthypalms. Results are discussed with the available literature onother similar disease caused by fungi, bacteria and mycoplasma-likeorganisms in different plants. Key words: Cocos nucifera L., Stomatal resistance, Root (wilt) disease