Persistent effects of seedling treatment on growth of sugar beet in pots

Further evidence is provided that the environment of sugar-beet seedlings, or growth substances applied to seedlings, continues to influence growth when the plants are later in other environments. Sugar-beet seeds were germinated at 20 °C in 8, 16 or 24 h photoperiods of constant light intensity, i.e. with different amounts of total radiation. When the seedlings had two leaves (15–18 days old) they were transferred to large pots in the glasshouse. Some seedlings were treated with (2-chloroethyltrimethylammonium chloride) either sprayed on the leaves or applied to the soil, at different times. The treatments affected areas of individual leaves throughout the growing period; plants raised in 24 h photoperiod had the largest leaves, and those in 8 h photoperiod the smallest. Consequently, 24 h plants had most dry matter and 8 h plants least. Plants given most radiation produced leaves fastest and CCC applied early increased the rate, but as the leaves were smaller, except late in 1967, and died sooner, the leaf area duration was less and so yields were less. CCC applied later did not affect leaf production. There was no interaction between amount of radiation and CCC treatment. Twenty-four hour plants had the greatest net assimilation rate (E) early. CCC decreased E early, but increased it later and more when sprayed on the leaves than when applied to the soil. Some factor, possibly pot size, eventually restricted growth and probably diminished the effect of the treatments applied to the seedlings.     

The Effect of Manganese on the Assimilation and Respiration Rate of Isolated Rooted Leaves

The effect of manganese on carbon assimilation, respiration,and translocation has been studied using isolated rooted potatoleaves and small potato plants. Methods are described for therooting and culture of the leaves and plants. It was found thatnormal potato leaves rooted readily when treated with -naphtha-leneaceticacid (2 p.p.m.), but that very few of the manganese-deficientleaves produced roots, the critical level being about 15 p.p.m.manganese on a dry weight basis. The growth of isolated deficientleaves was also much less than that of control leaves, but inno case did characteristic manganese-deficiency symptoms develop,although the manganese level had fallen below that of leaveswhich showed symptoms when attached to the plant. A marked differencein net assimilation rate was found between leaves which hada high or low manganese content at the time of rooting. Theaddition of manganese after rooting to low manganese leavesdid not, however, cause an increase in assimilation rate, althoughthe manganese content of the leaves had been raised to thatof the control leaves. Manganese was shown to have only a smalleffect on respiration, higher respiration rate being consistentlyassociated with a higher manganese content; the addition ofmanganese to ‘deficient’ leaves did not cause anyincrease in respiration. No effect of manganese on translocationwas detected.     

The Mobility of Manganese in the Wheat Plant: II. Redistribution in Relation to Concentration and Chemical State

Wheat plants were grown in solution culture at two levels ofmanganese supply until the second leaves were fully expanded.The supply of manganese was then curtailed and symptoms of deficiencyappeared in subsequent growth. Although redistribution of manganeseat rates dependent upon initial content occurred in both high-and low-manganese plants, first and second leaves always retainedsufficient for normal function, and remained healthy. In a secondexperiment no redistribution from the second leaves was observedunder similar conditions of supply and demand. When second leaves were killed and placed in water, up to 80per cent, of the manganese diffused out, but extraction of similarleaves with 80 per cent, methanol removed only 15—20 percent, of that present. These results suggest that the lack ofmobility shown by the element is not due to precipitation orcomplex formation within the tissue, although at high levelsof manganese supply the solubility of manganese silicate mightbe exceeded, and some precipitation may occur.     

THE EFFECT OF MANURES ON THE BOLTING OF THE BEET PLANT

In sugar beet, the effect on bolting of additions of potash manures, of superphosphate, and of the mixture of these was not significant, whether applied at the time of sowing or previously. Dung applied in the previous autumn slightly increased the number of plants which went to seed, and when applied just before sowing it had a more marked effect. An amount of sulphate of ammonia which would have approximately the same stimulating effect as the dung gave a slightly larger amount of bolting.
On red beetroot, it was possible to compare larger and smaller dressings of various coarse organic manures, and of each of these with and without dressings of sulphate of ammonia. In all cases the sulphate of ammonia and each of the organic manures largely increased the amount of bolting, and a doubling of the organic manure dressing or the addition of sulphate of ammonia to it caused a further increase. Sewage sludge gave an abnormally large amount of bolting, but it is doubtful whether this was due to the larger amount of organic matter and nitrogen applied in this manure. In general, any manurial addition causing more vigorous growth leads to an increase in bolting. There is a very large variation in the amount of running to seed in the crop of red beetroot from different parts of the same field, but the effect of the manures on the proportion which bolted was not widely different.
The general question as to the reason why beet plants should bolt more in one season than in another is discussed, and it is suggested that a check to the plants in an early stage, whether caused by dryness or waterlogging, or by low temperature, followed by a vigorous growing period may have something to do with the matter. This would agree with the experiences recorded in the present paper.     

The Effect of Applying a Nutrient in Leaf Sprays on the Absorption of the Same Nutrient by the Roots

Ammonium nitrate solution applied to the leaves of sugar-beetincreased plant dry weight and uptake of nitrogen by the roots.Uptake of phosphorus by the roots of swedes, but not sugar-beet,grown with high phosphorus supply to the roots, was decreasedby applying sodium phosphate solution to the leaves; uptakefrom a lower phosphorus supply to the roots was unaffected.Phosphorus applied to the leaves had no effect on dry weight.Potassium uptake by the roots of sugar-beet plants grown withhigh potassium supply to the roots was unaffected by paintingthe leaves with a potassium chloride solution, that of plantswith an intermediate potassium supply was increased, and plantsgrown with a low supply to the roots absorbed almost all theavailable potassium so painting could not much increase uptakeby the roots. Application of potassium to the leaves increaseddry weight of plants with low or medium potassium supply tothe roots and did not affect that of plants with a high potassiumsupply. The top: root ratio for phosphorus content in mg. per plantwas greater for phosphorus absorbed via leaves than for phosphorusabsorbed via roots. Increasing the phosphorus supply to theroots increased this ratio for phosphorus absorbed either vialeaves or roots. Potassium absorbed by leaves was slightly more efficient inincreasing dry weight than potassium absorbed at the same timeby the root. A similar comparison was not possible for nitrogenor phosphorus. The results of these and previous experiments indicate thatall the nitrogen and potassium and over 80 per cent. of thephosphorus applied to leaves was absorbed. The small amountof phosphorus remaining unabsorbed on the surface of the leafwas unaffected by phosphorus supply to the root.     

Immunocytochemical evidence for a peroxisomal localization of manganese superoxide dismutase in leaf protoplasts from a higher plant

The controversial question of the intracellular location of manganese-containing superoxide dismutase in higher plants was examined under a new experimental approach by applying the more rigorous and specific methods of immunocytochemistry to protoplasts isolated fromPisum sativum L. leaves. Manganese superoxide dismutase (EC 1.15.1.1) was purified to homogeneity from 15 kg of leaves ofPisum sativum L. Rabbits were immunized with the mangano enzyme and the antibody specific for pea manganese superoxide dismutase was purified and found not to contain antigenic sites in common with (i) human manganese superoxide dismutase, (ii) iron superoxide dismutase from eitherEscherichia coli or higher plants, or (iii) plant or animal cuprozinc-superoxide dismutase.Pisum sativum L. manganese superoxide dismutase only appears to have antigenic determinants similar to other manganese superoxide dismutases from higher land plants. The antibody to pea Mn-superoxide dismutase was used to locate the enzyme in protoplasts isolated from young pea leaves by indirect immunofluorescence, and by electron microscopy using the unlabelled antibody peroxidase-antiperoxidase method. Results from immunofluorescence showed that chloroplasts were devoid of specific fluorescence which appeared scattered over the cytosolic spaces among chloroplasts, and demonstrate the absence of manganese superoxide dismutase inside chloroplasts. The metalloenzyme was found to be localized only in peroxisomes, whereas mitochondria, the traditionally accepted site for this enzyme in many eukaryotic organisms, did not show any specific staining. The possible subcellular roles of manganese superoxide dismutase inPisum sativum L. leaves are discussed in the light of its peroxisomal location.     

Effect of manganese toxicity on the indoleacetic Acid oxidase system of cotton

The effect of substrate manganese on tissue manganese levels and activity of the indoleacetic acid (IAA)-oxidase system of cotton (Gossypium hirsutum, L.) was investigated. A sand culture technique was used with 1, 3, 9, 27 and 81 mg manganese (MnSO₄) per liter nutrient solution applied in various experiments.

The following relationships held for both long-term (126 days) and short-term (12-14 days) exposures to manganese treatment: A) There was a direct relationship between substrate and tissue manganese. B) Only the 81 mg/liter Mn plants exhibited severe manganese toxicity symptoms. C) At the toxic level of manganese an increased IAA-oxidase activity and decreased IAA-oxidase inhibitor activity was observed. There was a direct relationship between degree of enzyme response and severity of visible symptoms. D) With the manganese toxicity plants, but none of the other treatments, extracts of the young leaves contained as much IAA-oxidase activity as extracts of much older leaves. E) Crude extracts from the plants grown with 81 mg manganese per liter solution, in contrast to those of other treatments, destroyed IAA without addition of MnCl₂ to the assay medium.

A hypothesis is advanced stating that manganese toxicity symptoms in cotton are expressions of auxin deficiency caused by IAA-oxidase activity increased by the abnormal tissue levels of manganese.

     

The Relative Toxicity of Manganese and Cobalt to the Tomato Plant

1. At equivalent concentrations, cobalt was more effective thanmanganese in inducing chlorosis and necrosis in tomato plants. 2. Chlorotic plants suffering from either cobalt or manganesetoxicity alone, or from the two conditions together, containedas much or more iron than normal plants, and chlorotic leavesresponded positively to painting with a solution of ferroussulphate. 3. When cultures were supplied with 5 p.p.m. Mn, distinct injuryof the lower leaves occurred regardless of the cobalt supply,but the addition of cobalt up to 0·01 p.p.m. broughtabout a gradual decrease in the chlorosis of the top leavesand an increase in dry weight. 4. With cobalt at the 0·1 p.p.m. level, severe chlorosisand necrosis occurred and growth was stunted, but by raisingthe manganese level to 5·0 p.p.m. a substantial antidotingeffect on the toxicity was obtained. 5. Cobalt and manganese had an antidoting effect on each other,whereby at high manganese supplies small quantities of cobaltalleviated manganese toxicity, while toxic concentrations ofcobalt were antidoted by high levels of manganese.     

Effect of Fe 3+, Zn 2+ and Mn 2+ on ferric reducing capacity and regreening process of the peach rootstock Nemaguard (Prunus persica (L.) Batsch)

The peach rootstock Nemaguard is susceptible to lime-induced iron deficiency chlorosis. Under field conditions, application of ferric chelates to the soil is effective in correcting the Fe-deficiency symptoms. The objectives of this work were to study the induction of the root ferric reducing capacity and the relationship between chlorosis and leaf Fe concentration of plants grown hydroponically under different treatments. Results showed that bicarbonate-treated plants grown with a low Fe concentration increased their reducing capacity if they received additional Fe or Zn for a short period (15 h). However, the addition of Mn had no effect. When these Mn-treated plants were changed to nutrient solution with no bicarbonate and sufficient Fe, regreening was retarded several days in relation to the other treatments. In plants grown without bicarbonate, the reducing capacity was higher in plants grown with a low amount of Fe than in plants grown with either 0 Fe or sufficient Fe. In plants grown with bicarbonate and low Fe, the leaves became chlorotic and had low Fe concentration. When these plants received higher Fe supply, the regreening of the old leaves was not complete, though they had even higher Fe concentrations that the new developing leaves which were completely green. Results are discussed in relation to the Fe or Zn requirements of plants to induce reducing capacity and the incapacity of the cells from chlorotic leaves to absorb Fe and repair metabolic and structural damages.     

锰有效性对大豆锰、铁和磷吸收及其分布的影响

本文研究外源锰有效性对大豆生长和锰、铁、磷吸收及其分布影响的结果表明,在锰缺乏和锰浓度超过50μmol·L-1的处理条件下,大豆生长受到明显抑制。随着外源锰浓度增加,大豆体内,尤其在老叶中锰浓度显著增加。锰和铁之间存在一定的拮抗作用。缺锰和锰毒不影响大豆对磷的吸收。但是,缺锰显著影响磷在老叶和新叶中的分配。     

Modification of growth habit of Majestic potato by growth regulators applied at different times

The effect of gibberellic acid, CCC (2-chloroethyltrimethylammonium chloride) and B 9 (N-dimethylaminosuccinamic acid) was studied on growth of potato plants in pots. Growth was analysed on four occasions and changes in habit defined in terms of internode lengths, leaf areas and growth of lateral branches. Soaking seed pieces for 1 hr. in GA solution caused six internodes to elongate greatly, an effect not prevented by CCC applied when the shoot emerged from the soil. The effects on internode extension were determined by the length of the interval between GA treatment and CCC treatment. Treatment at emergence with CCC shortened all internodes and more CCC applied 4 weeks later had no effect. Late application of CCC or B9 shortened the top two lateral branches, usually very long in untreated plants. The regulators affected leaf growth differently from internode growth: usually growth regulators had less effect on leaf growth. Effects on growth depended on when the regulators were applied. Treatment with GA alone inhibited bud development at higher nodes than in untreated plants; when followed by late treatment with CCC, lateral growth at higher nodes was also less. CCC retarded development of lateral branches especially when applied early. B9 had a similar effect to CCC applied late. When regulators retarded growth of lower laterals, upper laterals often grew more than in untreated plants. Treatments did not affect the number of leaves on the main stem at first but later GA hastened senescence. GA increased the number of leaves on lateral stems, and the effect was enhanced by CCC. CCC alone increased the number of first- and second-order lateral leaves. GA lengthened and CCC shortened stolons. The effect of CCC persisted throughout the life of the plant. CCC or B 9 shortened stolons whenever applied. CCC hastened tuber initiation but slowed tuber growth. CCC at first retarded formation of lateral tubers but had no effect on the ultimate numbers of lateral and terminal tubers. The value of E (net assimilation rate) did not alter with time. CCC applied at emergence increased E, probably because it hastened tuber initiation and temporarily increased sink capacity. Although tubers formed earlier with CCC, their growth was slower and their demand for carbohydrate was also less. The increase in second-order laterals in CCC-treated plants indicates that they utilize carbohydrate that would normally go to tubers. This experiment also demonstrates that crowding leaves by shortening stems did not diminish E, possibly because another over-riding process (bigger sinks) offsets the effect of shading.     

Manganese deficiency in sugar beet and the incorporation of manganese in the coating of pelleted seed

Summary A laboratory study, three glasshouse tests and eight field experiments on commercial farms in East Anglia during 1972 to 1974 tested the effect of incorporating manganese in the coating of pelleted seed on the manganese nutrition and yield of sugar beet. The pelleting material readily absorbed manganese from solution but most of the manganese was held in plant-available forms. Tests in the glasshouse showed that manganese sulphate or manganous oxide were likely to be the most effective seed-pellet additives, but manganese sulphate was harmful to sugar beet in slightly acid potting compost.Incorporating manganous oxide in the pellet prevented early symptoms of deficiency on sugar beet in field experiments and replaced an early foliar spray but the plants developed manganese deficiency later. The treatment was an economic and effective method of supplying manganese to sugar-beet seedlings too small to spray but, should manganese deficiency be prolonged, the plants will need spraying when large enough.     

Fatty-acid-induced release of manganes from chloroplasts

The effect of both endogenous and exogenous unsaturated free fatty acids on manganese release from chloroplasts of chill-resistant (spinach) and chill-sensitive (tomato, bean) plants was studied. The level of endogenous free fatty acids increased 2–3-fold during cold and dark storage of leaves of chill-sensitive plants and was accompanied by depletion of about 60% of total chloroplast manganese content. Similar effects were observed when accumulation of free fatty acids in chloroplasts was achieved by storage of growing tomato plants for a few days in the dark at room temperature. In contrast, the cold and dark treatment of leaves of chill-resistant plant (spinach) affected neither free fatty acid, manganese levels nor Hill-reaction activity in chloroplasts. Incubation of chloroplasts of both chill-sensitive and chill-resistant plants with bean leaf galactolipase resulted in an accumulation of free fatty acids and a release of approx. 60% of total manganese content. The same amount of total manganese content was released following 3 h incubation of chloroplasts with linolenic acid at fatty acid/chlorophyll ratio (w/w, 2:1–10:1). The efficiency of C₁₈ unsaturated fatty acids/linolenic, linoleic, oleic on manganese release from chloroplasts was established in decreasing order C_18:3 > C_18:2 > C_18:1. The results indicate that the inhibitory effect of both endogenous and exogenous fatty acids on Hill reaction depends on the release from chloroplasts of functionally active, loosely bound manganese. Thus, similarly to both Tris and hydroxylamine treatments of chloroplasts, the incubation of chloroplast preparations with unsaturated fatty acids may be a useful tool for manganese depletion of chloroplasts.     

Studies in the Nutrition of Apple Rootstocks The Effect on Growth and Mineral Composition of Supplying Iron Through the Leaves

Apple rootstocks were grown with either 0.02 ppm Fe (Fe₀) or5 ppm (Fe₃), to give very chlorotic or dark-green plants. Toinvestigate whether iron can be supplied through leaves insteadof roots the shoots of half the plants in each treatment weredipped periodically in solutions of iron. This prevented chlorosisin Fe₀ plants and increased their growth, which did not, however,equal that of Fe₃ plants supplied with iron through the roots.Growth of Fe₃ plants was reduced by dipping. Iron was not translocated from leaves to roots, although theconcentration in leaves was greatly increased by dipping. Dippingreduced the amount of manganese in Fe₀ roots to one-quarterof that in roots of undipped Fe₀ plants. Effects of treatmentson nitrogen, potassium, calcium, magnesium, and copper levelsare also described.     

Manganese deficiency of sugar beet in organic soils

Summary The manganese content of sugar beet grown in pots of organic soils taken from fields where crops regularly show symptoms of manganese deficiency, and the effects on it of foliar sprays of manganous sulphate and of manganous oxide or manganese silicate frit applied to the soil, of changing the soil pH, air-drying the soil, and growing the plants either in the glasshouse or outside were determined. All the manganese treatments increased the concentration of manganese in the plants and decreased deficiency symptoms, but increased the dry matter yield only slightly. Increasing the pH by liming greatly increased symptoms and decreased the manganese concentration in the dry matter; air-drying the soil before cropping had the opposite effect. Plants grown in pots of the same soil in the glasshouse or outdoors showed similar symptoms and had similar manganese content.The concentration of manganese in the leaves was related to the percentage of plants with deficiency symptoms and to the concentration of active soil manganese. Leaves usually had symptoms when the concentration of manganese in the dried leaves was less than 30 ppm, and always had severe symptoms when they contained less than 15 ppm Mn. The soil analyses suggest that sugar beet grown in organic soil with pH greater than 7.0 and containing less than 40 ppm active soil manganese is likely to show deficiency symptoms.     

Auslösung der Blütenbildung bei der Langtagpflanze Hyoscyamus niger im Kurztag durch 2-Thiouracil

Summary Aqueous solutions of 2-thiouracil (TU) were applied selectively either to the growing point or to the leaves of the long-day plant Hyoscyamus niger in order to determine whether this antimetabolite has an effect on the synthesis of the floral stimulus in the leaves. Applications to the growing point were made by means of a small glass tube covering the shoot apex; application to the leaves was performed by vacuum infiltration. In all experiments all leaves except the three youngest fully expanded leaves and the 8–10 youngest primordia were removed before application. Plants were recorded as having initiated flowers when flower primordia were visible under a dissection microscope 5 weeks after the experiment.TU was inhibitory to photoperiodic induction by long-days of 16 hours when applied to the growing point during the second 8 hours of the daily photoperiod. A concentration of 5·10^-3 M of TU fully suppressed flowering without significant inhibition of leaf primordia increment; however, leaves developing from treated primordia had reduced leaf blades. These results are in agreement with findings already published by other investigators.However, when the leaves were infiltrated by TU, the antimetabolite did not inhibit photoperiodic induction but on the contrary initiated flowering even under short-day conditions. This effect was investigated in more detail by repeated daily infiltrations of TU-solutions in concentrations of 10^-5–10^-2 M during the second part of an 8 hour photoperiod up to 5 following days. Even after one single infiltration of a 10^-4 M solution 18% of the treated plants were flowering; the percentage of flowering plants increased with increasing concentrations of TU and number of days of application up to approximately 80%. In no case was a flower initiation of 100% obtained. Leaves developing from primordia after infiltration of the leaves with TU have reduced and deformed leaf blades, indicating that TU is transported to the shoot apex to some extent.Some possible explanations of this inductive effect of TU were tested experimentally. Oxygen uptake of the leaves was not decreased and the respiratory quotient was not affected by TU. Photoperiodic induction is not stimulated by low concentrations of TU when applied to the growing point. Infiltration of the leaves by solutions of 2,4-dinitrophenol (10^-4 M) and sodium azide (10^-3 M) had no inductive effect under short-day conditions; a single complete defoliation (except for the 8–10 youngest primordia) is also not inductive. Under short-day conditions additional leaves remaining on the plant that were not infiltrated by TU decreased the percentage of flowering plants but did not fully suppress flower initiation.From these results it is concluded that TU does not act by inhibition of particular metabolic processes concerned in flower initiation or by inhibition of the synthesis of an inhibitor. We suggest that application of TU may lead to synthesis of a floral stimulus in the leaves under short-day conditions also.     

Enhancing phytoremediative ability of Pisum sativum by EDTA application

The aim of our research was to demonstrate how the presence of EDTA affects resistance of pea plants to Pb and Pb-EDTA presence, and to show the effectivity of lead ions accumulation and translocation. It was determined that EDTA not only increased the amount of Pb taken up by plants but also Pb ion transport through the xylem and metal translocation from roots to stems and leaves. It can be seen in the presented research results that addition of the chelator with Pb limited metal phytotoxicity. We also demonstrated a significant effect of EDTA not only on Pb accumulation and metal transport to the aboveground parts but also on the profile and amount of thiol compounds: glutathione (GSH), homoglutathione (hGSH) or phytochelatins (PCs), synthesized by the plants. We observed a significant effect of the synthetic chelator on increasing the level of Pb accumulation in roots of plants treated with Pb including EDTA (0.5 and 1 mM). Pisum sativum plants treated only with 1 mM Pb(NO3)2 accumulated over 50 mg Pb x g(-1) dry wt during 4 days of cultivation. Whereas in roots of pea plants exposed to Pb+0.5 mM EDTA 35% more Pb was observed. When 1 mM EDTA was applied roots of pea accumulated over 67% more metal. The presence of EDTA also increased metal uptake and transport to the aboveground parts. In pea plants treated only with 1 mM lead nitrate less than 3 mg Pb x g(-1) dry wt was transported, whereas in P. sativum treated with Pb-EDTA doubled amount of Pb was observed in stems and leaves.     

Water Stress in Plants

The abscisic acid (ABA) content was determined quantitatively in the leaves from wilted and unwilted tomato plants (Lycopersicon esculentum Mill. CV. Revermun) by the use of the wheat coleoptile test and gas-liquid chromatography (GLC). Plants which have received an insufficient daily water supply for 18 days showed adaptation to wilting conditions. The plants adjust to the added amount of water by regulating their water loss through transpiration. The concentration of ABA was not higher in the leaves of plants adapted to water stress than in plants that were watered abundantly. Wilted detached leaves and leaves from rapidly wilted intact plants showed the well-known reaction by increasing the ABA level. A possible role of ABA in the early stages of the adaptation process is discussed.     

Influence of washing on elemental analysis of leaves of fieldgrown crop plants

Summary Information is limited on soil contamination of leaves from field-grown row crops, especially with respect to aluminum (Al) analyses. The objective of this study was to determine the influence of washing leaf samples with either deionized water or detergent solution on elemental analyses for several agronomic crop plants. The crop plants sampled were corn (Zea mays L.), soybean (Glycine max L. Merr.), grain sorghum (Sorghum bicolor L. Moench), and wheat (Triticum aestivum L.). The crops were grown on a range of soil types, soil pH values, and tillage practices. Samples of upper leaves and lower leaves were collected separately. The samples were either not washed, washed with deionized water, or washed with detergent solution. After drying, grinding, and digesting, the samples were analyzed for Al, nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), magnesium (Mg), iron (Fe), manganese (Mn), zinc (Zn), and copper (Cu). For all crop plants and conditions studied, there was no effect on measured N, P, K, Ca, Mg, Mn, Zn, or Cu concentrations, but measured Al and Fe concentrations were influenced by washing. In general, washing had a greater effect on Al analyses than on Fe analyses. Soybean samples were most affected by washing, while wheat samples seemed to be least affected. The results reflected greater contamination of lower leaves than upper leaves. Decontamination procedures appear necessary prior to Al and Fe analyses of field-grown crop plants.     

THE EFFECT OF GIBBERELLIC ACID ON LEAF AREA AND DRY-MATTER PRODUCTION IN MAJESTIC POTATO

When gibberellic acid (50 p.p.m. in aqueous solution) was sprayed twice or six times at weekly intervals on potato plants (var. Majestic) with a low or high nitrogen supply it did not affect rate of leaf production on the main axis, but caused earlier senescence of leaves, especially with the more frequent spraying, and inhibited leaf production and growth on laterals of the high-nitrogen plants at nodes 10 and 11 but not at other nodes. This central region of the stem appears to have a low growth potential, probably because it lies midway between two zones of active growth, viz. the basal branches and the younger leaves on the main stem. Competition between these is increased by gibberellic acid. Gibberellic acid increased leaf area even when lack of nitrogen was restricting growth but this did not produce extra dry matter. Tuber weight was increased more in high-nitrogen plants by two sprayings than by six sprayings. The net assimilation rate of low-nitrogen plants was halved by spraying but was not changed in high-nitrogen plants where the value was similar to that of low-nitrogen control plants. The high-nitrogen plants had absorbed nearly all the available nitrogen between the second and third harvests, but plants treated with gibberellic acid, nevertheless, had more total dry weight and tuber dry weight than the controls. The nitrogen content of the leaves expressed on an area basis was lower in sprayed plants and, with continued spraying, fell at the third harvest to equal that of low-nitrogen plants. Evidently, the effect of gibberellic acid depended on the interaction between the rate of application and the nitrogen supply, but further work is necessary to define the conditions that give the maximal effect on dry-matter production.