Benzyladenine-Directed Transport of Carbon-14 and Phosphorus-32 in Senescing Bean Plants

The distribution of radioactivity from applied sucrose.¹⁴C and³²P to various plant parts were studied in relation to the retardationof leaf senescence by applied benzyladenine (BA) in intact beanplants. In short-time experiments sucrose-¹⁴C was fed to theplants for 48 h through the second trifoliate leaf at weeklyintervals from the third to the eighth week after planting.In long-term experiments sucrose-¹⁴C was fed to all plants for48 h at the third week and changes in distribution examinedat weekly intervals up till the eight week. In both cases, BAapplied to the primary leaves of intact bean plants did notcause a directed mobilization of sucrose-¹⁴C. When the plantswere stripped, leaving the primary leaves and the terminal pod,and fed sucrose-¹⁴C or ³²P through the terminal leaflet of thesecond trifoliate leaf, the BA-treated leaf accumulated relativelymore radioactivity than the opposite water-treated leaf. Itwas concluded that the retardation of senescence by BA in theprimary leaves of intact bean plants does not result directlyfrom the mobilization of metabolites and nutrients from otherplant parts. It is therefore suggested that BA-induced longevityin the primary leaves of the intact plant is accomplished bymetabolic self-sustenance.     

Rooting of Chrysanthemum Stem Cuttings as Affected by (2-chloroethyl) Phosphonic Acid and Indolebutyric Acid

Stem cuttings of Chrysanthemum morifolium Ram. were treatedwith aqueous solutions of (2-chloroethyl)phosphonic acid (Ethrel)and indolebutyric acid (IBA). Ethrel (1 mg per 1) as a dip oras two foliar sprays, promoted root length and branching inMrs. Roy and Clipper which are difficult-to-root cultivars,but had no effect on Improved Mefo, an easy-to-root cultivar.IBA increased root number in both Clipper and Improved Mefo.The results suggest that IBA and Ethrel act at different stagesof the rooting process, with IBA promoting initiation and Ethrelstimulating elongation and branching. Increases in root numberwith IBA treatment, and in root length with Ethrel treatment,were accompanied by decreases in the soluble carbohydrate concentration,particularly in stem bases.     

Absorption of Foliar-Applied 32P by Successive Leaves, and Distribution Patterns in Relation to Early Fruiting and Abscission in the Cowpea (Vigna unguiculata L.)

In controlled environment experiments, the uptake and distributionpatterns of ³²P were studied in relation to flowering and fruitingin the cowpea. Absorption by the plant, retention by the fedleaf, and translocation to various plant parts depended on theposition and age of the fed leaf. At the 4-leaf stage, whenthe terminal leaflet of the first trifoliate (oldest) was fed³²P, the plant absorbed 43 per cent of total radioactivity suppliedin 24 h. The percentages resulting from the feeding of trifoliates2, 3, and 4 (youngest) were 58, 71, and 73 respectively. Trifoliate1 retained 34 per cent of the total radioactivity, while trifoliate4 retained 68 per cent. Of the plant tissues, the root accumulatedthe greatest amounts of the P exported by the fed leaflet, withthe feeding of trifoliates 1, 2, or 3. With the feeding of trifoliate4, however, the root imported only 0.2 per cent of total radioactivity. When the plants had one set of flowers fully open at raceme1, the flowers imported 0.19 per cent of total radioactivityin the cultivar Adzuki, and 0.36 per cent in the cultivar EarlyRamshorn. When the raceme 1 flowers developed into fruits whilethe raceme 2 flowers were fully open, the raceme 1 fruit importof radioactivity was 2.61 per cent in Adzuki and 14.21 per centin Early Ramshorn. Raceme 1 fruits of Early Ramshorn thus accumulatedfive times as much P radioactivity as those of Adzuki. Whenracemes 1 and 2 both bore fruits, removal of the raceme 1 fruitsjust prior to ³²P feeding, led to the import by the raceme 2fruits of 0.25 per cent in Adzuki and 0.09 per cent in EarlyRamshorn. The raceme 1 fruits constituted a more potent sinkfor ³²P in Early Ramshorn than in Adzuki. The results are discussedin relation to the known patterns of premature abscission offlowers and young fruits in the two cultivars.     

Effects of 2-Chloroethyl Trimethylammonium Chloride (CCC) and 2-Chloroethylphosphonic Acid (CEPA) on Dry Matter Distribution in the Cowpea (Vigna Unguiculata L.)

Effects of foliar applications of CCC and CEPA on dry matterdistribution in two cowpea cultivars which exhibit differentdegrees of premature abscission of fruits were investigated.At the concentration of 0-1 mg1^–1, CCC increased stemweight in the cultivar Adzuki, but had no effect on the cv.Mala (which exhibits a relatively high degree of premature abscission).While CCC did not significantly influence root weight in Adzuki,the concentrations of 1 and 10 mg 1^–1 increased root weightin Mala. In both cultivars, the 1000 mg1^–1 treatment decreasedseed weight, with a greater decrease in Adzuki. All concentrations of CEPA, up to 1000 mg 1^–1, decreasedstem and root weights in Mala, and leaf weight in Adzuki. The10 mg1^–1 concentration increased seed weight in Mala by100 percent, and leaf weight by 28 percent, without any significanteffect on pod weight, or on the weight of the whole plant. Therewas also no increase in pod number. Overall, Mala was more responsive than Adzuki to the growthregulators, particularly CEPA. In the low concentration responses,CEPA increased seed weight not by increasing gross plant weight,but mainly by causing a change in distribution of dry matter.     

Vegetative Growth Responses of Pea Plants to CCC and Phosfon in Relation to Phosphorus Nutrition

The effects of 2-chloroethyltrimethylammonium chloride (CCC)and 2,4-dichlorobenzyl-tributylphosphonium chloride (Phosfon)on the growth of pea plants in sand culture at two rates ofapplied phosphorus (P), were studied in controlled-environmentgrowth chambers. CCC at 1 and 10 mg/1, and to a lesser degreePhosfon at 0.1 mg/1, stimulated growth. CCC at 1000 mg/1 andPhosfon at 100 mg/1 retarded growth, due mainly to shortenedstems. The magnitude of such effects depended on the level ofapplied P. Reductions in plant height by the 1000 mg/1 CCC treatmentwere 13 and 50 per cent respectively at the high (160 mg/1)and low (8 mg/1) rates of applied P. Similar decreases due to100 mg/1 Phosfon were 30 and 57 per cent respectively. At thehigh P rate, both CCC and Phosfon had no significant effecton total uptake of P, or on relative distribution in the leaf,stem, and root. At the low P rate, the root, relative to leafand stem, retained more P, at a CCC concentration of 1000 mg/1.With Phosfon at 100 mg/1 relative leaf P content increased whilethat of the stem and root decreased. Phosfon was more activethan CCC in terms of the concentration required to cause a givenmagnitude of growth effect.     

Effects of Phosphorus Nutrition and Light Intensity on Growth and Development of the Cowpea (Vigna unguiculata L.)

The vegetative growth and fruiting of two cowpea cultivars,Adzuki and Early Ramshorn, were studied in controlled environmentexperiments, using two light intensities and three P levelsin sand and in soil media. The higher light intensity reducedplant height, but improved plant growth in terms of increasedbranching, leaf area, plant size and seed yield. High lightintensity delayed flowering, but increased blossom and pod numbers. Increasing levels of applied P enhanced growth, blossom andfruit numbers, as well as leaf numbers and area and earlinessof flowering. Generally, Early Ramshorn plants grew faster andproduced heavier seeds than Adzuki plants, especially at highP. However, Adzuki plants produced greater numbers of flowers,pods and seeds than did Early Ramshorn plants. Under high lightintensity, Adzuki produced the greatest number of seeds at theintermediate P level in sand culture, and this number was greaterthan that produced by Early Ramshorn at the highest P level. In Adzuki, P nutrition did not markedly modify the adverse effectof low light intensity on pod set and mature pod number, anindication of a lower external P requirement and/or higher efficiencyof P utilization than in Early Ramshorn. Phosphorous generallyincreased growth rate and yield and could thus be used to offsetsome of the adverse effects of low light intensity especiallyon Early Ramshorn as well as to hasten growth and maturation.The results obtained with soil culture were similar to thosewith sand culture.     

Effects of Benzyladenine on Photosynthesis, Growth and Senescence of the Bean Plant

The net photosynthetic rate of attached primary bean leaves treated with benzyladenine (BA) decreased from 35 nano-grams carbon dioxide per square centimetre and second (ng cm^?2 s^?1) at week 2 to 17 ng cm^?2 s^?1 at week 4, and thereafter increased to 24 at week 6. By contrast the net photo-synthetic rate of the water-treated leaves decreased to 4–5 ng cm^?2 s^?1 at weeks 5 and 6. The stomatal resistance was not markedly affected by BA treatment. The BA-treated primary leaves had higher dry and specific weights, and the chlorophyll and carotenoid contents were greater than for the water controls. The pigment content of the BA-treated leaves steadily increased from week 2 to 6, whereas in the water controls it remained constant till week 4 and thereafter decreased. It is concluded that retardation of leaf senescence by BA is assoclatcd with a mnintenance of photosynthetic activity.     

Effects of 2-Chloroethylphosphonic Acid on Growth, Plastid Pigments, and Sucrose Translocation in Radish

2-Chloroethylphosphonic acid (CEPA) caused a significant declinein chlorophyll content of radish plant within 5 d of treatment.Such effects were greater when plants were treated at the two-than at the four-leaf stage. In early treated plants, concentrationof CEPA increasing from 20 mg/1 progressively increased leafweight, while decreasing root (radish) weight. A concentrationof 10 mg/1, applied at the three-leaf stage, increased leafand root weights by 27 and 30 per cent respectively in the cultivar‘Cavalier’. Similar responses were obtained withthe cultivar ‘Cherry Belle’. While Cavalier showeda discrete 10 mg/1 optimum, ‘Cherry Belle’ exhibiteda range of concentrations (10-40 mg/1) optimal for growth. At relatively high concentrations, early application of CEPAcaused inverse changes in sucrose-¹⁴C in the leaves and theroot, so that decreased retention by leaves was accompaniedby increased transport to roots. Low concentrations of CEPAappear promising for growth stimulation in root-crop plants.     

Effects of Gibberellic Acid, Benzyladenine and 2-Chloroethylphosphonic acid (CEPA) on Growth and Fruit Abscission in the Cowpea (Vigna unguiculata L.)

Cowpea cultivars, Adzuki, Ife Brown and New Era, were raisedin a pot-soil experiment, under greenhouse conditions. Whenapplied as a foliar spray, none of the three growth regulators,gibberellic acid (GA), benzyladenine (BA) and 2-chloroethylphosphonicacid (CEPA), had any significant effects on the vegetative growthof either Adzuki or Ife Brown, CEPA, however, suppressed stemelongation and root dry weight, and also caused defoliation,in New Era. GA had no significant effect on fertility (defined as the proportionof the number of floral buds to those developing into mature,functional, seed-bearing pods). GA also had no significant effecton harvest index (expressed as the percentage of whole plantdry weight represented by seed dry weight) in the three cultivars.BA suppressed fertility in both Ife Brown and New Era, but hadno influence on Adzuki. CEPA was effective in controlling abscission in cowpea by reducingthe number of floral buds initiated, but enhancing the numberof functional pods set, in New Era. CEPA also enhanced harvestindex in this cultivar by increasing the absolute seed weightwithout affecting total plant dry weight. The implications ofthese observations on the physiology of the cultivars are discussedin relation to the problem of fruit abscission in the cowpeaplant. Vigna unguiculata L., cowpea, abscission, gibberellic acid, benzyladenine, 2-chloroethylphosphonic acid     

Distribution of 14C Assimilates in the Cowpea (Vigna unguiculata L.) in Relation to Fruit Abscission and Treatment with Benzyladenine

The distribution of ¹⁴C assimilates from ¹⁴C-sucrose was studiedin relation to premature fruit abscission in two cowpea cultivars,Adzuki and Mala. In both cultivars most of the radioactivitywas recovered in the fruits, constituting 63–85 per centof the total ¹⁴C imported from the fed leaflet. This was followedby the root, leaves and stem in descending order, except thatin Mala, import by the stem was greater than that by the leaves.Adzuki imported 56 per cent more ¹⁴C than Mala, from the fedleaflet. In Adzuki, which exhibits a relatively low degree ofabscission of young fruits, the ratio of ¹⁴C accumulated bypeduncle 1 (oldest) fruits to that of peduncle 3 (youngest)fruits was 0·31; while in Mala it was 0·61. Ratiosof the combined accumulation by peduncles 1 and 2 fruits topeduncle 3 fruits were 0·81 for Adzuki, and 1·88for Mala. The more mature fruits of Mala thus constituted amore potent sink for ¹⁴C assimilates than those of Adzuki. In Adzuki, benzyladenine treatment of young fruits at each pedunclewas not significantly effective in reversing or modifying thenormal gradient of assimilates in fruits of different ontogeny.However, in Mala, BA treatment of the youngest fruits caused43 per cent increase in ¹⁴C import, when compared with correspondingfruits of control plants. In Adzuki, BA had no significant effecton total fruit weight, whereas in Mala the weight was increasedby about 36 per cent.