Modification of flag leaf senescence and yield characters in barley (Hordeum vulgare L.) by gibberellic acid and kinetin

Barley plants (Hordeum vulgare L.) received foliar applications of 10^?4 M gibberellic acid (GA₃) and Kinetin (KN) individually and in combination at one or more of three growth stages: flag leaf appearance (I), ear emergence (II), and the first stage of senescence initiation in the flag leaf (III). Both plant growth regulators (PGR) hastened onset of senescence when sprayed at Stage I and/or Stage II. Treatment at Stage III, either alone or in combination with treatments at the other stages, tended to postpone senescence. Yield components also showed stage-dependent response: Stage I treatment increased the formation of total and bearing tillers, and Stage III treatment improved grain number and weight. However, while GA₃ proved more effective than KN, the two together acted antagonistically.     

Hormones-induced modifications in the response of wheat flag leaf to NaCl

A field experiment was carried out to investigate the effects of presoaking the wheat grains (Triticum aestivum L.) in 33 or 66 mM NaCl and indolyl-3-acetic acid (IAA at 50 g m⁻³), gibberellic acid (GA₃ at 100 g m⁻³) or kinetin (100 g m⁻³) on some tolerance criteria in wheat flag leaf at different stages of development. At various stages of flag leaf development pretreatment with 33 or 66 mM NaCl decreased degree of succulence (particularly 66 mM), relative growth rate, net assimilation rate, relative water content, K⁺ content and K⁺/Na⁺ ratio and at the same time induced accumulation of abscisic acid and Na⁺. In the majority of cases grain pretreatment with GA₃ or kinetin and to a lesser extent with IAA alleviated either partially or completely the deleterious effect of salinity on the above mentioned parameters.     

Culture of Shoot Apices of Theobroma cacao

Surface sterilized buds of young cocoa plants (Theobroma cacao L.) taken at particular stages of the flush cycle were placed in Linsmaier and Skoog agar medium supplemented with a range of growth regulators. Only buds taken at the 1–2 (dormant) stage of the flush cycle and treated with gibberellic acid (GA₃) alone and GA₃plus kinetin (KN) supplement showed bud opening. In liquid Linsmaier and Skoog medium buds isolated at the 1–2 stage also responded to GA₃ and KN. In this case addition of KN caused bud opening, while GA₃ either initiated bud opening only or opening followed by leaf expansion depending on the concentration of GA₃ supplied. Bud development was inhibited when ABA was included in the medium hut this was overcome by the presence of GA₃ but not KN. Since a hormonal supplement was required for any response from the excised buds, it is suggested that the intermittent growth of the shoot apex in the intact plant may be determined by hormonal stimuli derived from other parts of the plant. The findings also indicate that the bud apices could be maintained in culture for long periods which may provide a basis for the development of a micropropagation procedure for cocoa.     

Growth and pigment content of wheat as influenced by the combined effects of salinity and growth regulators

A field experiment was conducted to investigate the effects of presoaking the wheat grains (Triticum aestivum L.) in different levels of salinity (33 or 66 mM) and in growth regulators (indolyl-3-acetic acid, IAA at SO g m^-3, gibberellic acid, GA₃ at 100 g m^-3, or kinetin at 100 g m_-3) on the shoot growth and pigment content of the developing wheat flag leaf. Salinity at 33 or 66 mM led to an insignificant increase in the fresh and dry masses as well as in the shoot diameter and shoot length, but it attenuated the flag leaf area. In the majority of cases, salinity increased the chlorophyll (Chla, Chlb) and carotenoid contents as well as the number of chloroplasts per a mesophyll cell. The growth in the wheat shoot of the saline-treated plants was, in general, stimulated in response to presoaking the grains in kinetin or GA₃. On the other hand, IAA + salinity led to a negligible effect on the growth in the wheat plants particularly at the early stages of growth. The presoaking of grains in NaCl at 33 mM + IAA or 66 mM + kinetin induced a marked increase in the pigment content of the wheat flag leaf particularly at the early stages of growth. The interaction between salinity and phytohormones increased the number of chloroplasts; kinetin was the most effective.     

The Effects of Gibberellin4+7 on the Vase Life and Flower Quality of Alstroemeria Cut Flowers

Leaf yellowing is a major problem in Alstroemeria and absence of leaf senescence symptoms is an important quality attribute. Two Alstroemeria cultivars ‘Yellow King’ and ‘Marina’ were sourced from a commercial farm and harvested when sepals began to reflex. Stems were re-cut under water and kept in vase solutions of gibberellin A₄₊₇ (0, 2.5, 5.0, 7.5, 10.0, 12.5 or 15.0 mg l⁻¹ [Provide^r]). Treatments and cultivars were combined in a factorial fashion and arranged in a completely randomised design. Application of GA₄₊₇ in the holding solution at 2.5–10.0 mg l⁻¹ significantly delayed the onset of leaf senescence by around 7 days and significantly increased days to 50% petal fall by ca. 2 days. Additionally, these GA₄₊₇ concentrations resulted in higher retention of leaf nitrogen, leaf chlorophyll and also increased leaf water content, while reducing leaf dry weight, all relative to untreated controls. Cultivar ‘Yellow King’ had significantly longer vase life and a better retention of leaf quality than ‘Marina’. Our results suggest that a concentration of 10 mg l⁻¹ GA₄₊₇ can be used to prolong vase life, delay leaf senescence and enhance post-harvest quality of Alstroemeria cut flowers during their transport to market.     

ABA and GA3 affect the growth and pigment composition in Andrographis paniculata Wall.ex Nees., an important folk herb

In this study, 5 μmol·L⁻¹ abscisic acid (ABA) and gibberellic acid (GA₃) were used to study the effect of both growth regulators on the morphological parameters and pigment composition of Andrographis paniculata. The growth regulators were applied by means of foliar spray during morning hours. ABA treatment inhibited the growth of the stem and internodal length when compared with control, whereas GA₃ treatment increased the plant height and internodal length. The total number of leaves per plant decreased in the ABA-treated plants, but GA₃ treatment increased the total number of leaves when compared with the control. Both growth regulators (ABA and GA₃) showed increased leaf area. ABA and GA₃ treatments slightly decreased the total root growth at all the stages of growth. The growth regulator treatments increased the whole plant fresh and dry weight at all stages of growth. ABA enhanced the fresh and dry weight to a larger extent when compared with GA₃. An increase in the total chlorophyll content was recorded in ABA and GA₃ treatments. The chlorophyll-a, chlorophyll-b, and carotenoids were increased by ABA and GA₃ treatments when compared with the control plants. The xanthophylls and anthocyanin content were increased with ABA and GA₃ treatments in A. paniculata plants.     

Effect of Indol-3-yl Acetic Acid on Photosynthetic Characteristics of Wheat Flag Leaf During Grain Filling

Area and fresh and dry masses of flag leaf show two phases of development during grain filling in Triticum aestivum. The initial large increase in leaf size is mainly due to water intake. Contents of chlorophylls and carotenoids, reducing sugars, and sucrose, Hill reaction rate, and photosynthetic activity increased during leaf growth, but a noticeable decline in these parameters followed throughout leaf senescence. The maximum accumulation of polysaccharides and proteins occurred at the beginning of grain set, but a continuous decline in their absolute values was manifested during grain filling. Grain priming with indol-3-yl acetic acid (IAA) at 25 mg kg^-1 stimulated the flag leaf growth, namely its fresh and dry masses and its area. Furthermore, the stimulatory effect was mainly due to the increase in the pigment formation that in turn increased the photosynthetic activity of flag leaf during grain filling. On the other hand, the highest dose of IAA (50 mg kg^-1) attenuated the growth and physiological activity of flag leaf through its inhibitory action on leaf fresh and dry masses, leaf area, pigments, saccharides and protein formation, as well as its effect on ¹⁴CO₂ assimilation.     

Migrations Orientées et Phytohormones — Valeur de la Feuille Détachée comme Matériel Expérimental

Directed Transport and Hormones — Value of Isolated Leaf as Experimental Material. Local application of aqueous phytohormonal solution (0.1 ml of various concentrations, from 50 to 0.025 mg-l^?1, of IAA, 2,4-D, NAA, BAP, GA₃) on isolated leaves influences the direction of ion transport. All tested hormones are efficient but the action depends upon the ionic species [positive action with ³²P, ³⁵S, ³⁶Rb (K), but null with ⁴⁵Ca or ⁴⁶Cl]. The movement of ions occurs through the phloem tissue and is not a cell-to-cell transfer. Competition between different parts of the leaf is demonstrated (a) between petiole which appears to be an important attractive centre and other parts of the leaf; (b) in a depetioloted leaf, between different centres induced by different phytohormones. In this respect, GA₃ appears to be the most efficient hormone in the tested material — leaves of Pelargonium zonale (L.) Aiton. The effects on directional transport are discussed in relation to other processes controlled by hormones, for instance growth, senescence, protein synthesis. A direct relation of directional transport with growth or delay of senescence may be discarded. The value of isolated leaves as simplified experimental systems is underlined by the fact that weak hormonal doses are efficient (0.025 mg.l for GA₃ and 0.5 mg.¹ for 2,4-D) as compared to the higher doses used in other plant systems.     

Effect of growth regulators onVicia faba plants irrigated by sea water Leaf area,pigment content and photosynthetic activity

The antagonistic effects of some growth regulators [i.e. indol-3-yl-acetic acid (IAA), gibberellic acid (GA₃) or kinetin] on stress imposed by sea water on leaf area, pigment and photosynthetic activity in leaves of broad bean plants at different stages of development were investigated. Seed priming with GA₃ alleviated either partially or completely the effects induced by the two levels of sea water (10 and 25 %) used on leaf area at all experimental stages. However, IAA, GA₃ and kinetin inhibited leaf growth by themselves in almost all measurements. Seed pretreatment with kinetin alleviated the inhibition of pigment production in sea water-irrigated plants. Furthermore, GA₃ or kinetin nullified the deleterious effects imposed by irrigation with sea water particularly the high level (25 %) on photosynthetic¹⁴CO₂ fixation.     

Interrelationship between ethylene and growth regulators in the senescence of lettuce leaf discs

The interrelationship between ethylene and growth regulators in the senescence of romaine lettuce (Lactuca sativa L.) leaves was studied. Gibberellic acid (GA₃), kinetin, and 3-indoleacetic acid (IAA) retarded chlorophyll loss from leaf discs which were floated on hormone solutions. Abscisic acid (ABA) and ethephon enhanced chlorophyll loss and antagonized the senescence-retarding effect of GA₃ and kinetin. A high concentration of IAA (10^–4 M) caused accelerated chlorophyll loss, whereas a similar concentration of kinetin neither retarded nor promoted chlorophyll loss. The ineffectiveness of IAA and kinetin at their supraoptimal concentrations in retarding leaf senescence was related to increased production of ethylene induced in the treated leaf discs. GA₃ was the most effective in retarding chlorophyll loss and did not stimulate ethylene production at all. The senescence-enhancing effect of ABA was not mediated by ethylene. However, the moderately increased production of ethylene, induced by relatively high concentrations of ABA, could act synergistically with the latter to accelerate chlorophyll loss. It is proposed that the effectiveness of exogenously applied hormones, both in enhancing and retarding senescence, is greatly affected by the endogenous ethylene concentration of the treated plant tissue.Contribution from the Agricultural Research Organization, The Volcani Center, Bet Dagan, Israel, No. 2571-E, 1988 series.     

Proteomic analysis of berry-sizing effect of GA3 on seedless Vitis vinifera L

Gibberellin (GA) is widely used in the table grape and raisin industries to enlarge the berries of seedless varieties. However, the mechanism underlying its berry‐sizing effect is poorly understood. In this study, clusters of Centennial Seedless (Vitis vinifera L.) were treated with 30 ppm GA₃ on day 12 after flowering, and berries were sampled at development stages I, II and III for proteomic analysis. Among the 1479 proteins detected on 2‐DE maps, 19, 70 and 69 spots in stages I, II and III, respectively, showed an at least twofold difference in volume between treatments and controls. Of these, 125 proteins were successfully identified and assigned to eight functional groups, chief among them are metabolism and energy, stress response, expression regulation and cytoskeleton proteins. Stress‐response proteins were predominantly down‐regulated in GA₃‐treated berries in stages I and II, and significantly up‐regulated in stage III. Up‐regulation of cytoskeleton, cell‐wall modification and other important proteins was found in the two latter stages of berry development. Our proteomic results and subsequent validation revealed, for the first time, the role of redox homeostasis in GA₃‐induced berry enlargement and markedly remodeled cellular protein expression in treated berries.     

Gibberellins in Leaves of Alstroemeria hybrida: Identification and Quantification in Relation to Leaf Age

In alstroemeria (Alstroemeria hybrida), leaf senescence is retarded effectively by the application of gibberellins (GAs). To study the role of endogenous GAs in leaf senescence, the GA content was analyzed by combined gas chromatography and mass spectrometry. Five 13-hydroxy GAs (GA₁₉, GA₂₀, GA₁, GA₈, and GA₂₉) and three non-13-hydroxy GAs (GA₉ and GA₄) were identified in leaf extracts by comparing Kováts retention indices (KRIs) and full scan mass sprectra with those of reference GAs. In addition, GA₁₅, GA₄₄, GA₂₄, and GA₃₄ were tentatively identified by comparing selected ion monitoring results and KRIs with those of reference GAs. A number of GAs were detected in conjugated form as well. Concentrations of GAs in alstroemeria changed with the development of leaves. The proportion of biologically active GA₁ and GA₄ decreased with progressive senescence and the fraction of conjugated GAs increased. Received May 26, 1997; accepted August 12, 1997     

Soil salinity effects on transpiration and net photosynthetic rates,stomatal conductance and Na+ and Cl− contents in durum wheat

Leaf gas exchange, plant growth and leaf ion content were measured in wheat (Triticum durum L. cv. HD 4502) exposed to steady- state salinities (1.6, 12.0 and 16.0 dS nr⁻¹) for 8 weeks. Salinity reduced leaf area and number of tillers, and increased Na⁺ and Cl⁻ concentrations in leaves. Leaf- to- leaf gradients of these ions were observed. The oldest leaf contained 6 to 8 times more Na⁺ and Cl⁻ than the flag leaf. Net photosynthetic rate (P_N), transpiration rate (E) and stomatal conductance (g_S) were the highest in flag leaf, declined in the middle and fully expanded leaves, and were minimum in the oldest leaves. These processes were reduced by salinity with similar leaf- to- leaf gradients. Intercellular CO₂ concentrations in the older leaves were higher than in the flag leaf in non-saline plants, and increased similarly with salinity. Leaf age was the major factor in reducing P_N, and senescence processes were promoted by salinity.     

Endogenous gibberellin levels and senescence in Taraxacum officinale

Summary The level of endogenous gibberellins (GAs) in leaf tissue of Taraxacum officinale was high during leaf growth and expansion but declined progressively during leaf senescence. In the chromatographic system used, most of the GA from Taraxacum leaves moves with the R_f of GA₃. However, several other GAs were also effective in retarding senescence in Taraxacum leaves. It is concluded that ageing of dandelion leaves is associated with a deficiency of endogenous GA.     

The Effect of Boron and Gibberellic Acid on the Senescence of Leaf Discs from Lycopersicon esculentum cv. Rutgers

When leaf discs of Lycopersicon esculentum Mill. cv. Rutgers were floated on solutions containing 4.33 × 10^–6 M gibberellic acid (GA₃), 1.0 ×x 10^–6M boron (B), separately and together, senescence was retarded with respect to controls. Degradation of chlorophyll, total protein, RNA, and DNA was delayed, and decreases in fresh weight and leaf disc diameter checked. The loss of chlorophyll, protein, RNA, DNA, fresh weight, and diameter were 10, 20, 30, 8, 28, and 0 per cent with GA₃ alone; 15, 25, 35, 8, 31, and 0 per cent with B alone; 8, 14, 25, 7, 25, and 0 per cent with GA₃ plus B; contrasted with 50, 40, 50, 9, 42, and 3 per cent for the controls. An analysis of variance was performed on all data except for disc diameter. All sources of variance were significantly or highly significant at the 1 per cent level except for the effect of boron on DNA level, which was significant only at the 2.5 per cent level. Retardation of senescence by GA₃ may be associated with the known ability of GA₃ to stimulate m-RNA and protein synthesis. The effect of boron may be due to an effect on sugar and starch balance, translocation of sugar, or on water balance, but more likely boron plays a role in nucleotide and protein metabolism in plants. Boron may be involved in the synthesis of DNA, a role perhaps mediated by GA₃.     

Mechanism of monocarpic senescence in rice

During grain formation stage (90 to 110 days), the youngest flag leaf of rice (Oryza sativa L. cv. Jaya) remained metabolically most active (as indicated by cellular constituents and enzyme activities) and the third leaf the least active. At the grain development stage (110 to 120 days) the above pattern of age-related senescence of the flag leaf completely changed and it senesced at a faster rate than the second leaf which remained metabolically active even up to grain maturation time (120 to 130 days), when both the flag and the third leaf partially senesced. Removal of any leaf temporarily arrested senescence of the remaining attached leaves, that of flag leaf did not hasten senescence of the second leaf, while that of either the second or the third accelerated senescence of the flag. Removal of the inflorescence after emergence or foliar treatment of intact plant with kinetin equally delayed senescence and produced an age-related, sequential mode of senescence or leaves. Both translocation and retention of ³²P by the flag leaf were maximum at the time of grain formation and that by the second leaf was maintained even up to grain maturation time. The induction of senescence of the flag leaf was preceded by a plentiful transport of ³²P to the grains. Kinetin treatment decreased the transport of ³²P, prolonged its duration, and almost equally involved all of the leaves in this process. The pattern of senescence of isolated leaf tips was similar to that of attached leaves. The level of endogenous abscisic acid-like substance(s) maintained a close linearity with the senescence behavior of the leaves of intact and defruited plants during aging, and the rise in abscisic acid in the flag leaf was also preceded by higher ³²P transport to the grains.     

Micropropagation of sweet viburnum (<Emphasis Type="Italic">Viburnum odoratissimum</Emphasis>)

A micropropagation protocol for shoot culture of sweet viburnum (Viburnum odoratissimum) is described. Nodal explants, initially established on MS medium, were transferred to WPM supplemented with combinations of BA and GA₃. Maximum shoot multiplication was observed on explants cultured on medium supplemented with BA concentration higher than 1.1 μM, and 14 μM GA₃. Although Stage II medium supplemented with BA concentration higher than 1.1 μM resulted in increased shoot multiplication, it also caused a decrease in shoot length. A negative carry over effect of GA₃ on rooting was observed in subsequent Stage III cultures. The presence of GA₃ in Stage II medium promoted shoot elongation, but it also caused a decrease in microcutting rooting. For this reason, 0.5 μM BA and 14 μM GA₃ were selected for optimum Stage II shoot multiplication. Although 100% microcuttings formed roots when cultured on medium containing 6.0 μM NAA, significant callus formation was observed and ex vitro survival rate was low (49%). Rooting was achieved after 3 weeks with 82% of microcuttings on medium supplemented with 3 μM IBA. The survival rate of plantlets under ex vitro conditions was 100% after 3 weeks. Plants looked healthy with no visually detectable phenotypic variation based on observation of about 30 plants.     

Comparison of phosphorus mobilization during monocarpic senescence in rice cultivars with sequential and non-sequential leaf senescence

The senescence pattern of the three uppermost leaves of four rice (Oryza sativa L.) cultivars viz. Ratna, Jaya, Masuri and Kalojira was analysed in terms of decline of chlorophyll and by measuring [³²P]-phosphate retention and export from leaf to grains during the reproductive development. With the advancement of reproductive development, the cultivars Masuri and Kalojira showed a sequential mode of senescence, but the cultivars Ratna and Jaya showed a non-sequential mode of leaf senescence where the flag leaf senesced earlier than the older second leaf. Foliar spraying with benzyladenine (0.5 mM) significantly delayed, and abscisic acid (0.1 mM) accelerated, leaf senescence. In untreated control plants, the second leaf had the highest export of labelled phosphate among the leaves at the grain formation stage (0–7 days) in Masuri and Kalojira. This was compensated by the flag leaf at the grain development stage (7–14 days), whereas export of [³²P]-phosphate was highest from the flag leaf of Ratna and Jaya at the grain development stage. Compared with the control, benzyladenine treatment caused higher retention of [³²P]-phosphate in the leaves and also export to the grains, but abscisic acid treatment gave lower retention and export of [³²P]-phosphate to the grains. The amount of [³²P]-phosphate export from a mother to a daughter shoot developed in the axil of the second leaf of plants with the panicle removed, was less than that to panicles remaining on control plants of all cultivars. When the panicle had been excised, the greatest export of [³²P]-phosphate took place from the second leaf to the daughter shoot in all cultivars. Excision of the panicle delayed leaf senescence as compared with intact controls and maintained an age-related leaf senescence pattern in all the four cultivars. The results presented here demonstrate that mobilization of phosphorus from leaf to grains, regardless of cultivar or age and position of the leaf, correlates well with the senescence of that leaf.     

Carboxypeptidases of germinating triticale grains

Presence of five carboxypeptidases was found in endosperm of germinating triticale grains, while two of them in scutellum. Changes of their activities during four days of germination suggest that carboxypeptidase II plays an important role at initial stage of germination, while carboxypeptidases I and III - at subsequent stages of the process. High activity of carboxypeptidase II both in scutellum and endosperm of dry grains accompanied by its decrease during germination, and on the other hand, the appearance of carboxypeptidases I and III activities at the 2^nd and 3^rd day of the process seems to confirm such functions of these enzymes. Experiments with GA₃ indicated that carboxypeptidase I was synthesized in scutellum, and carboxypeptidase III — in aleurone layer. Carboxypeptidases I and II cleave N-CBZ-Phe-Ala, and carboxypeptidase III — N-CBZ-Ala-Met and N-CBZ-Ala-Phe as substrates with the highest rate.     

Amino acid metabolism associated with N-mobilization from the flag leaf of wheat (Triticum aestivum L.) during grain development

Field-grown winter wheat (Triticum aestivum L. cv. Castell) was used to study changes in the free amino acid pools of different plant parts and related enzyme activities in the flag leaf throughout the grain-filling period in three consecutive growing seasons. Amino acid analysis data indicated that, during senescence, the nitrogen flow in the flag leaf was directed towards the synthesis of glutamine as a specific nitrogen transport form. Of the enzymes involved, total glutamine synthetase (GS; EC 6.3.1.2) and especially ferredoxin-dependent glutamate synthase (Fd-GOGAT; EC 1.4.7.1) activities declined continuously as senescence progressed. Unlike (chloroplastic) GS₂, (cytosolic) GS₁ was shown to be very persistent suggesting a special role for this isoenzyme in the N-reallocation process. Glutamate-oxaloacetate transaminase (GOT; EC 2.6.1.1), glutamate-pyruvate transaminase (GPT; EC 2.6.1.2) and isocitrate dehydrogenase (IDH; EC 1.1.1.42) showed a characteristic biphasic activity profile after anthesis. It is proposed that these enzymes, for each of which at least two isoenzymes were demonstrated, are involved in glutamate synthesis at the later stages of leaf senescence. Ammonium levels were fairly constant throughout the flag leafs life span, an ultimate rise often following peak values of glutamate dehydrogenase (GDH; EC 1.4.1.4) activity. The enzymology of flag leaf amino acid metabolism during grain development is further discussed in relation to observations of NH₃-volatilization from naturally senescing wheat plants.