Boron Deficiency in Unfertilized Cotton ( Gossypium hirsutum ) Ovules Grown in Vitro

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Cotton ovules cultured in an insufficiency of boron (10 micromolar), showed inhibition of fiber growth by the ninth day in culture. Averaging data from eight to eleven days of culture under these conditions, total incorporation of 16-4Clorotic acid into fiber was inhibited by 59%. Inhibition was evident in all radioactively labeled pools, indicating that the effect may be at the membrane transport level or at an early stage of orotic acid metabolism. On a per cent basis, incorporation into RNA under boron deficiency was higher than under sufficiency. The effect is greater on the eighth day of culture, with a decreasing difference from controls up to the eleventh day. Conversely, the per cent incorporation into UDP-glucose was lower under boron deficiency than in controls, having a more or less constant value from 8 to 11 days of culture. Thus, a prinary event of boron deficiency in cotton fiber culture is an alteration in the flow of metabolites through the pyrimidine synthesis pathway.A possible primary event of boron deficiency is the influence of boron on pyrimidine metabolism. A Robertson and Loughman (18,19) for Vicia roots where elongation was being inhibited but had not ceased. In recent studies, Chapman and Jackson (6, 13), working with Phaseolus root tips, showed both early and late effects. There was an early (6-10 h) increased uptake of ["C]-uridine or [32Plinorganic phosphate into RNA at a time when the RNA levels were unchanged. RNA levels fell only after root elongation ceased (100 h) concurrently with manifestation of other boron deficiency symptoms. Increased ribonuclease activity may accompany the decrease in RNA in boron-deficient tissues (6,25).Information about the influence of boron on nucleotide levels is very sparse (4,5,28). Robertson and Loughman (18,19) Working with the in vitro-cultured cotton fiber system, Birnbaum et al. (21) found that the OMP'-decarboxylase inhibitor, 6-azauracil gave symptoms resembling those caused by boron deficiency (3). The correlation was further strengthened by the finding that low uracil concentrations partially overcame both boron deficiency and 6-azauracil effects, presumably by utilization of the uracil salvage pathway.In the present study, we sought to establish more directly whether boron regulates the pyrimidine pathway in some way. Our experimental tissue was fiber from the cotton ovule culture system. We studied the incorporation of [14CJOA into intermediates of the pyrimidine pathway. A factor which had to be taken into account was the possible effect of boron deficiency on OA uptake by the tissue itself.A defmitive study on the interaction of boron with ion transport mechanisms has been done by Loughman's group (14, 16-19), using mainly V. faba seedlings at a stage where root elongation was inhibited by boron deficiency but had not totally ceased. They discovered that the reduced uptake of [32P]phosphate and other inorganic ions caused by boron deficiency, actually involves several components including translocation, metabolism, inter...

Section: Methodsmentioning

confidence: 99%

Pyrimidine Pathway in Boron-deficient Cotton Fiber

Wainwright

Palmer²,

Dugger³

1980

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“…Birnbaum et al (3) reported that boron appears to be involved in elongation of fibers developing on excised, unfertilized, hormonally stimulated, cotton ovules grown in vitro. It is presently unclear what relationship these tissues and this system have to those employed in the present study.…”

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confidence: 99%

Effect of Boron on Cell Elongation and Division in Squash Roots

Cohen

Lepper

1977

This work establishes that cessation of root elongation of intact squash (Cucurbita pepo L.) plants is an early result of boron deficiency. Root elongation is slowed by 6 hours and is virtually stopped as early as 24 hours after boron is first withheld from the nutrient solution. As root elongation ceased, cell elongation progressed distally into the region normally occupied by the apical meristem and eventually the meristem became indistinguishable. Differentiation was determined by use of an elongation index in which cell length was compared to cell width. This index ranged from a low of 0.8 in boron-sufficient root meristems to a high of 3 in root meristems grown in a boron-deficient nutrient solution for 98 hours. It is concluded that a continuous supply of boron is not essential for cell elongation but is required for maintenance of meristematic activity. Boron may act as a regulator of cell division in this tissue. treated and were grown in modified Shive nutrient solution containing boron (+B) as described by Albert and Wilson (1). On the 5th day, roots were washed and placed into either freshly prepared modified Shive nutrient solution to which boron was added (+B) or into nutrient solution without added boron (-B). Water for both types of solutions was obtained by passing distilled H2O through a Millipore Milli-Q2 system. Just before placing the plants into +B or -B nutrient solutions, two roots/ plant were marked by placing small India ink marks 10 mm from the root tip. Subsequent root elongation was determined by measuring the distance from the root tip to the mark. Net root elongation was determined after periods of 0,6, 12, 24, 48, 72, and 98 hr of +B and -B treatment and root tips were harvested for histological examination at these times. The terminal 1 cm of each root was excised, fixed in formaldehyde-acetic-acid-alcohol (6), dehydrated, embedded in paraffin, sectioned, and stained with Sharman stain (11).Alexander (2) studied the onset of boron deficiency in squash plants grown in solution culture in which boron was withheld. He examined the roots of boron-deficient plants after periods of 48, 72, and 98 hr of boron deficiency to observe histological effects of the treatment. After 48 hr of boron deficiency, he reported a decrease in the size of the root cap; collapsed, disintegrated, and enlarged cells or groups of cells in the peripheral portions of the stele; and differentiation close to the root meristem. Examination of roots after 98 hr of boron deficiency commonly revealed death of the extremities of the tip. In the region of elongation, individual cells could no longer be recognized. Varying degrees of response were observed in any given experiment.Other workers have questioned whether boron is necessary for either cell elongation or cell division. Alexander (2), Neales (7), and Sommer and Sorokin (8) beginning from the 5th day onward). Measurements made during the first 24 hr of boron deficiency are presented in Figure 1. All points represent means of at least 100 roots. At all...

“…If boron is omitted from this medium, growth is quite aberrant; little or no fiber is produced, and the inundated and peripheral surfaces of the ovules callus profusely, obliterating any semblance of normal morphology (4). The morphological and physiological processes of cotton fiber growth involve elongation and maturation of single epidermal cells.…”

mentioning

confidence: 99%

“…We have reported that development of boron deficiency symptoms in cultured cotton ovules is determined in part by the phytohormones included in the basal growth medium (4). Profuse callusing in the absence of boron occurs only in the presence of GA3.…”

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confidence: 99%

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Interaction of Boron with Components of Nucleic Acid Metabolism in Cotton Ovules Cultured in Vitro

Birnbaum¹,

Dugger²,

Beasley³

1977

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Cotton (Gossypium hirsutum L.) ovules grown in a defined nutrient medium undergo normal morphogenesis, induding fiber production. In identical medium lacking boron, ovules callus and accumulate brown substances. Boron deficiency-like symptoms were induced by 6-azauracil and 6-azauridine in ovules growing in boron-sufficient media. Other nudeoside base analogs either reduced or had no effect on over-all growth, but did not cause typical boron-deficient callus growth of cotton ovules. Orotic acid and uracl countered the effects of 6-azauracil. Actinomycin D, fluorodeoxyundine, and ethidium bromide reduced not only fiber production on ovules growing in boron-sufficient media but also callusing of ovules in boron-deficient media.Similarties between symptoms of boron deficiency and 6-azauracil injury, and the ability of uracil to suppress both, suggest that boron defciency symptoms are related to reduced activity in the pyrimidine biosynthetic pathway. Changes in nucleic acid levels have been correlated with boron deficiency. Some workers have reported that RNA levels increase during boron deficiency (8-10) while others have observed a decrease in nucleic acid levels (5, 7). Chapman and Jackson (7) found that an early sign of boron deficiency in Phaseolus aureus root tip segments was increased incorporation of radioactive precursors into RNA. Only later, concomitant with increased ribonuclease activity and cessation of elongation, did a reduction in RNA levels occur. They point out that reports of boron deficiency-related reductions in RNA were in grossly deficient tissues (1,18) and that a much earlier and possibly more direct effect of boron deficiency was increased RNA synthesis (8, 9).