Leaf expansion in Phaseolus: transient auxin-induced growth increase

Control of leaf expansion by auxin is not well understood. Evidence from short-term exogenous applications and from treatment of excised tissues suggests auxin positively influences growth. Manipulations of endogenous leaf auxin content, however, suggest that long-term auxin suppresses leaf expansion. This study attempts to clarify the growth effects of auxin on unifoliate (primary) leaves of the common bean ( Phaseolus vulgaris ) by reexamining the response to auxin treatment of both excised leaf strips and attached leaves. Leaf strips, incubated in culture conditions that promoted steady elongation for up to 48 h, treated with 10 μ M α-naphthalene acetic acid (NAA) responded with an initial surge of elongation growth complete within 10 h, followed by insensitivity. A range of NAA concentrations from 0.1 to 300 μ M induced increased strip elongation after 24 and 48 h. Increased elongation and epinastic curvature of leaf strips was found specific to active auxins. Expanding attached unifoliates treated once with aqueous auxin NAA at 1.0 m M showed both an initial surge in growth lasting 4–6 h followed by growth inhibition sustained at least as long as 24 h post-treatment. Auxin-induced inhibition of leaf expansion was associated with smaller epidermal cell area. Together, the results suggest increasing leaf auxin first increases growth and then slows growth through inhibition of cell expansion. Excised leaf strips retain only the initial increased growth response to auxin and not the subsequent growth inhibition, either as a consequence of wounding or as a consequence of isolation from the plant.     

Effect of Leaf Detachment on Chlorophyll Fluorescence during Chilling Experiments

The effect of leaf detachment on chlorophyll fluorescence was analyzed for Zea mays, Cucumis sativus, Phaseolus vulgaris, and Echinochloa crus-galli. Results clearly indicate that detachment hastens the decrease in chlorophyll fluorescence during the course of chilling experiments. For maize and bean, the activity of photosystem II of chloroplasts isolated from detached leaves is lower than that of chloroplasts isolated from attached leaves. There are also large differences in ionic loss between detached and attached leaves of barnyard grass which could correlate with changes in leaf water status. The detached leaves lost some 50% of their total ionic content. Finally, detachment alters the ranking of the species with regard to their chilling tolerance.     

Synergistic interactions between volicitin,jasmonic acid and ethylene mediate insect-induced volatile emission in Zea mays

Plants display differential responses following mechanical damage and insect herbivory. Both caterpillar attack and the application of caterpillar oral secretions (OS) to wounded leaves stimulates volatile emission above mechanical damage alone. Volicitin ( N- 17-hydroxylinolenoyl- l -glutamine), present in beet armyworm (BAW, Spodoptera exigua ) OS, is a powerful elicitor of volatiles in excised maize seedlings ( Zea mays cv. Delprim). We consider some of the mechanistic differences between wounding and insect herbivory in maize by examining the activity of volicitin, changes in jasmonic acid (JA) levels, and volatile emission from both intact plant and excised leaf bioassays. Compared to mechanical damage alone, volicitin stimulated increases in both JA levels and sesquiterpene volatiles when applied to intact plants. In a bioassay comparison, excised leaves were more sensitive and produced far greater volatile responses than intact plants following applications of both volicitin and JA. In the excised leaf bioassay, volicitin applications (10–500 pmol) to wounded leaves resulted in dose dependent JA increases and a direct positive relationship between JA and sesquiterpene volatile emission. Interestingly, volicitin-induced JA levels did not differ between intact and excised bioassays, suggesting a possible interaction of JA with other regulatory signals in excised plants. In addition to JA, insect herbivory is known to stimulate the production of ethylene. Significant increases in ethylene were induced only by BAW herbivory and not by either wounding or volicitin treatments. Using intact plant bioassays, ethylene (at 1 µl l⁻¹ or less) greatly promoted volatile emission induced by volicitin and JA but not mechanical damage alone. For intact plants, wounding, elicitor-induced JA and insect-induced ethylene appear to be important interacting components in the stimulation of insect-induced volatile emission.     

水分胁迫对棉花叶片中IAA从含量、IAA氧化酶和过氧化物酶活性的影响

整株干旱降低盐棉46号叶片中的IAA总量,叶龄愈小下降愈多。幼叶中IAA总量的下降主要是结合态IAA减少的结果。气干和-1.7MPa PEG溶液渗透胁迫处理也降低离体成熟叶片的IAA总量,其变化与叶片含水量呈直线相关(r=0.905)。整株干旱处理提高各叶片的过氧化物酶活性,叶龄愈小提高愈多,但IAA氧化酶活性无显著变化。离体和整株干旱时IAA总量的下降,可能是过氧化物酶活性增加所致。     

The Relationship between the Growth of the Primary Leaf and of the Coleoptile in Seedlings of Avena and Triticum

Partial inhibition of extension growth of the primary leaf occurswhen whole Triticum seedlings are immersed in aerated solutionsof IAA but is replaced by growth promotion when sucrose is addedto the external solution. In seedlings in which the coleoptilehas been excised, IAA increases the growth of the leaf bothwith and without additional sucrose. Inhibition of the leaf by moderate concentrations of IAA nolonger occurs when the seedling is detached from the endosperm.Sucrose added to the external solution raised the percentageelongation of the coleoptile almost to the level of that attainedin intact seedlings without additional carbohydrate. It alsoenabled the leaf to show a positive growth response with IAA. The results indicate that in intact seedlings treated with IAAthe growth of the primary leaf is markedly diminished owingto diversion of carbohydrate to the coleoptile if the growthof the latter is promoted as a result of the treatment. Whenthe competition of the coleoptile for carbohydrate is diminishedor eliminated, acceleration of the growth of the primary leafby IAA becomes apparent. In addition to the endogenous rhythm, with a period close to24 hours, induced in the growth-rate of the coleoptile whenseedlings of Avena are transferred from red light to darkness,a similar rhythm, with a slightly longer period, is inducedin the growth-rate of the primary leaf. This rhythm persistsin elongating leaves so long as they remain within the coleoptile.It can be recorded for at least 100 hours in deseeded seedlings. When intact seedlings of Avena are immersed for one hour inrelatively high concentrations of IAA and then transferred todistilled water for 18 hours, the elongation of the coleoptileis greater and the inhibition of the leaf is less than whenthey are transferred to humid air. Sections of the leaf of Triticum showed a slight increase inelongation in concentrations of IAA up to 5 mg./l., but no evidencewas obtained that sections of leaf and coleoptile exert any.influenceon each other's elongation when floated together on solutionsof IAA.     

Mechanical wounding and abscission in citrus

Fruit detachment force (FDF), ethylene evolution, fruit and leaf drop were determined in Citrus sinensis for periods up to 96 h after mechanical wounding. Injury by removing a thin section of mature fruit flavedo reduced FDF, increased ethylene evolution and promoted abscission. Injuring flavedo 1 cm below the calyx was more effective at reducing FDF than injuring flavedo at the equator or the blossom‐end of mature fruit. Injuring the calyx or peduncle of mature fruit, or injuring three leaves closest to the mature fruit did not reduce FDF. Immature fruitlets either did not abscise or underwent low rates of abscission in response to mechanical wounding, depending on age. Inhibiting ethylene binding in wounded mature fruit with 1‐methylcyclopropene (1‐MCP) increased ethylene evolution compared with wounded fruit alone, but the reduction in FDF was similar. When an ethylene biosynthesis inhibitor (aminoethoxyvinylglycine, AVG) was used, reduction in FDF of wounded mature fruit exposed to AVG was similar to that of wounded fruit alone but ethylene production was markedly reduced. Wounding mature leaf blades in the presence or absence of 1‐MCP resulted in elevated but equal ethylene evolution up to 48 h after wounding, however, no leaf drop occurred. Thereafter, ethylene evolution was higher in 1‐MCP‐treated wounded leaves. Removing up to 77% of the total mature leaf area did not cause leaf drop, nor did wounding tissue across the laminar or petiolar abscission zones. Leaflets of 5 mm length reached nearly 100% abscission after mechanical wounding, whereas wounding leaves 20 mm length resulted in 15% abscission. The data suggest that mechanical wounding of flavedo results in mature fruit abscission, and ethylene binding may not be mandatory to initiate abscission in citrus fruit. The differential response of fruit and leaves at different ages to wounding may be related to potential contribution to carbohydrate accumulation, and production and sensitivity of tissues to an abscission signal(s).     

Ethylene-induced leaf abscission in cotton seedlings : the physiological bases for age-dependent differences in sensitivity

The speed of ethylene-induced leaf abscission in cotton (Gossypium hirsutum L. cv LG-102) seedlings is dependent on leaf position (i.e. physiological age). Fumigation of intact seedlings for 18 hours with 10 microliters per liter of ethylene resulted in 40% abscission of the still-expanding third true (3°) leaves but had no effect on the fully expanded first true (1°) leaves. After 42 hours of fumigation with 50 microliters per liter of ethylene, total abscission of the 3° leaves occurred while <50% abscission of the 1° leaves was observed. On a leaf basis, endogenous levels of free IAA in 1° leaves were approximately twice those of 3° leaves. Free IAA levels were reduced equally (approximately 55%) in both leaf types after 18 hours of ethylene (10 microliters per liter) treatment. Ethylene treatment of intact seedlings inhibited the basipetal movement of [¹⁴C]IAA in petiole segments isolated from both leaf types in a dose-dependent manner. The auxin transport inhibitor N-1-naphthylphthalamic acid increased the rate and extent of ethylene-induced leaf abscission at both leaf positions but did not alter the relative pattern of abscission. Abscission-zone explants prepared from 3° leaves abscised faster than 1° leaf explants when exposed to ethylene. Ethyleneinduced abscission of 3° explants was not appreciably inhibited by exogenous IAA while 1° explants exhibited a pronounced and protracted inhibition. The synthetic auxins 2,4-D and 1-naphthaleneacetic acid completely inhibited ethylene-induced abscission of both 1° and 3° explants for 40 hours. It is proposed that the differential abscission response of cotton seedling leaves is primarily a result of the limited abscission-inhibiting effects of IAA in the abscission zone of the younger leaves.     

Induction and suppression of RNase activity by growth regulators in senescing ragi leaves

Activity of RNase was studied in attached and detached leaves of 7-day-old ragi ( Eleusine coracana Gaertn. cv PR 202) plants during senescence using crude enzyme extracts. The RNase activity was relatively constant in attached leaves. In excised leaves incubated in the dark there was a rapid rise in enzyme activity up to 48 h, followed by a decline. No such decrease was observed in the light. Benzimidazole and gibberellic acid suppressed the activity of RNase up to 48 h in the dark and 96 h in the light. Both the growth regulators also prevented the post-48 h decline in RNase activity of dark incubated excised leaves. Decline in the levels of chlorophyll and RNA in the illuminated excised leaves was not affected by 3-(3,4-dichlorophenyl)-1,1-dimethyIurea, but the inhibitor prevented the photo-induced rise in RNase activity. Cycloheximide and actinomycin D could completely prevent both detachment (increase in enzyme activity after the leaf is excised) and photo-induced rise in RNase activity. Benzimidazole and gibberellic acid prevented the rise in the activity of RNase on one hand and maintained it on the other by their influence on its biosynthesis. Photoinduction of RNase and photo-induced retardation of senescence are concluded to be two different processes.     

Some effects of supplying benzyladenine to leaves and plants inoculated with viruses

With tomato spotted wilt virus in petunia leaf strips, N-6 benzyladenine (BA) was as effective as kinetin in decreasing numbers of local lesions, a result which could not be attributed to an effect on the virus per se. Benzimidazole, adenine and ammonium nitrate were without effect. Benzyladenine was more effective than kinetin when supplied through the petioles of excised whole leaves. Local lesions and infectivity of TSWV in detached leaves of Nicotiana rustica were decreased by supplying BA before and after inoculation. Lesions and infectivity were also decreased in attached leaves when BA was applied 9 days before inoculation. BA supplied to attached leaves after inoculation increased infectivity. Supplying BA to the lower leaves of tomato plants before inoculating with TSWV decreased infectivity of unsprayed, systemically infected tip leaves taken as inoculum; BA supplied after inoculation increased infectivity. Local lesions caused by lucerne mosaic virus in excised leaves of Phaseolus vulgaris were decreased in number by supplying BA. The effects of pre- and post-inoculation sprays of BA are considered in relation to cell metabolism. Since pretreating leaves with kinins did not prevent infection, it is suggested that those which move freely through plants without adverse effects on normal growth may prove of value in increasing the tolerance of plants to virus infection.     

Effect of regurgitant from Leptinotarsa decemlineata on wound responses in Solanum tuberosum and Phaseolus vulgaris

The effect of regurgitant from Leptinotarsa decemlineata Say larvae on wound-induced responses was studied using two plant species, Solanum tuberosum L. and Phaseolus vulgaris L. Wounding of one leaf of intact S. tuberosum plants differentially affected ethylene production and activities of peroxidase and polyphenol oxidase. Only polyphenol oxidase activity was stimulated by wounding in both wounded and systemic leaves. Peroxidase activity was not affected by wounding. Wounding caused only a transient increase of ethylene production from wounded leaves. The application of regurgitant to wound surfaces stimulated ethylene production as well as activities of peroxidase and polyphenol oxidase in both wounded and systemic leaves. Wounding significantly enhanced ethylene production and polyphenol oxidase activity in wounded and systemic leaves of P. vulgaris . The application of regurgitant caused an amplification of ethylene production, peroxidase activity, and polyphenol oxidase activity, in both wounded and systemic leaves of bean plants. Several substances were tested for their role as possible endogenous signals in P. vulgaris . Hydrogen peroxide and methyl jasmonate appeared as potential local and systemic signals of ethylene formation in wounded bean plants. Local ethylene production in leaf discs was differentially affected by the regurgitant application in potato versus bean plants. While all tested concentrations of regurgitant caused stimulation of ethylene formation from potato leaf discs, ethylene production was completely inhibited by increasing concentrations of the regurgitant in bean leaf discs. Our data present evidence that ethylene may play an important role in the interaction between plants and herbivores at the level of recognition of a particular herbivore leading to specific induction of signalling cascades.     

Phospholipases Dα and δ are involved in local and systemic wound responses of cotton (G. hirsutum)

Phospholipases D (PLDs) catabolize structural phospholipids to produce phosphatidic acid (PtdOH), a lipid playing central role in signalling pathways in animal, yeast and plant cells. In animal cells two PLD genes have been studied while in model plant Arabidopsis twelve genes exist, classified in six classes (α-ζ). This underlines the role of these enzymes in plant responses to environmental stresses. However, information concerning the PLD involvement in the widely cultivated and economically important cotton plant responses is very limited. The aim of this report was to study the activity of conventional cotton PLD and its participation in plant responses to mechanical wounding, which resembles both biotic and abiotic stresses. PLDα activity was identified and further characterized by transphosphatidylation reaction. Upon wounding, cotton leaf responses consist of an acute in vitro increase of PLDα activity in both wounded and systemic tissue. However, determination of the in vivo PtdOH levels under the same wounding conditions revealed a rapid PtdOH formation only in wounded leaves and a late response of a PtdOH increase in both tissues. Εxpression analysis of PLDα and PLDδ isoforms showed mRNA accumulation of both isoforms in the wounded tissue, but only PLDδ exerts a high and sustainable expression in systemic leaves, indicating that this isoform is mainly responsible for the systemic wound-induced PtdOH production. Therefore, our data suggest that PLDα and PLDδ isoforms are involved in different steps in cotton wound signalling.     

The Metabolism of Oat Leaves during Senescence: II. Senescence in Leaves Attached to the Plant

The course of senescence in the first leaves of light-grown Avena seedlings when attached to the plant has been compared with that previously studied in detached leaves and leaf segments. Proteolysis in the leaf, whether attached or detached, is accompanied by markedly polar basipetal transport of amino acids. This polar transport can be superimposed on the known transport of amino acids towards a locally applied cytokinin. In the intact plant, it results in a strong movement into the roots. The reducing sugars, which are set free in senescence, do not participate appreciably in this polar transport phenomenon.     

Immunological Identification of Proteinase Inhibitors I and II in Isolated Tomato Leaf Vacuoles

Proteinase inhibitor I has been identified and quantified in isolated vacuoles from tomato (Lycopersicon esculentum) leaves induced to accumulate inhibitors either by wounding or by supplying excised leaves with the wound hormone, proteinase inhibitor-inducing factor. Proteinase inhibitor II was also identified in the vacuoles but not quantified. Control vacuoles were prepared from unwounded plants that did not contain inhibitors. Vacuole to leaf cell ratios of inhibitors, chlorophyll, and several vacuolar and cytoplasmic enzymes were determined. The inhibitors were found almost entirely in the vacuoles. Acid phosphatase was located in control leaf vacuoles, but was found in both vacuoles and cytoplasm in induced leaves. Carboxypeptidase, induced by wounding, was found distributed between the vacuoles and cytoplasm of induced leaves. Low vacuole to leaf cell ratios of three cytoplasmic markers, triosephosphate isomerase, catalase, and chlorophyll, indicated that the isolated vacuoles were relatively free of intact protoplasts and cell debris.     

The Effect of Root Formation on Photosynthesis of Detached Leaves

The CO₂ exchange of fully expanded detached primary leaves ofdwarf bean (Phaseolus vulgaris) with roots on the petioles hasbeen measured. Rates of apparent photosynthesis and respirationincreased as roots grew, decreased when roots were removed,and increased again as root regenerated. Rates of photosynthesisof different leaves were highly correlated with the dry weightof root on their petioles. Photosynthesis and respiration weredecreased when root growth was restricted by kinetin, and wereincreased when root growth was stimulated by IAA. Photosynthesisof an attached leaf declined with time while that of a comparabledetached leaf increased. The results suggest that photosynthesisis correlated with the size of the roots that are a sink forphotosynthates.     

Induction of Phenylalanine Ammonia-lyase in Strawberry Leaf Disks: Action Spectra and Effects of Wounding, Sucrose, and Light

The increase in phenylalanine ammonia-lyase (PAL) activity in strawberry (Fragaria vesca var. WSU-1232) leaf disks required wounding, sucrose, and light and was cycloheximide-sensitive. In injured leaves and in leaf disks, the highest PAL activity was detected nearest the wounded tissues. Without wounding, no increase in activity was observed when leaves were cultured in sucrose and light.     

Slight tissue wounding fails to induce consistent chemical defense in three willow (Salix spp.) clones

We studied the effects of natural wounding by insects and artificial wounding by clipping with scissors on the phenolic chemistry of two willows, Salix myrsinifolia and Salix pentandra. Half of the blade of a mature leaf was removed from each experimental plant either by allowing insects (chrysomellid beetles) to feed on the leaf or by clipping off half the blade of a leaf with scissors. We also examined the ability of wounded plants to warn neighboring plants of imminent wounding by an airborne signal by maintainign one set of control plants in the room containing the wounded plants and another set of control plants in a room hermetically sealed from the room containing the wounded plants. After 48 h, the experimental leaf and the fourth leaf and eighth leaf upwards in the leaf sequence from the experimental leaf were analyzed for phenols by high-pressure liquid chromatography. The same leaves in the leaf sequence from each control plant were similarly analyzed for phenols. Only one phenol, salicortin in leaves of S. myrsinifolia, increased in concentration in response to defoliation, and the observed response was small. The type of wounding affected this increase in salicortin, with natural wounding by insects causing a greater response than artificial wounding in one S. myrsinifolia clone, and artificial wounding causing a greater response than insect wounding in the other clone. This result indicates that S. myrsinifolia cannot control the effects of diffeeent types of wounding on its leaf secondary chemistry. We also found no indication of airborne warning signals between wounded and unwounded plants that trigger an elevation of leaf defenses in unwounded plants in anticipation of herbivore attack.     

Fast upward propagation of the wound signal that systemically elevates phosphatidic acid

Phosphatidic acid (PA) increases in response to wounding at the neighboring unwounded leaf as well as at the wounded leaf of many plants (Lee et al., 1997). This indicates that a signal propagates from the wounded leaf to its neighboring leaves. In this paper, we report the speed and direction of propagation for a systemic wound signal that elevates PA. When a leaf of a soybean (Glycine max) seedling at the 2-leaf-stage was wounded, the PA level of the neighboring leaf did not change within the first min, but did increase significantly in 2 min, returning to the control level after 15 min. This implies that the systemic wound signal was generated at least within 2 min of wounding, and was propagated at a speed of at least 10–16 mm/min. When we wounded individual leaves of soybean and tobacco (Nicotiana tabaccum) seedlings that had 3 or 4 leaves, PA levels were elevated only in the younger leaves located above the wounded leaf, but not in the older, lower leaves. Thus, the PA-elevating wound signal preferentially moves upward in these plants.