Effect of Boron on the Incorporation of Glucose from UDP-Glucose into Cotton Fibers Grown in Vitro

Abstract

Boron is required for fiber growth and development in cotton ovules cultured in vitro. Incorporation of I''Clglucose by such fiber from supplied UDP-j''Clglucose into the hot alkali-insoluble fraction is rapid and lnear for about 30 minutes. Incorporation of I''Clglucose from such substrate by fibers grown in boron-deficient ovule cultures is much less than in the case with fibers from ovules cultured with boron in the medium. Total products (alkali-soluble plus alkali-insoluble fractions) were also greater in fibers from ovules cultured with boron. The fraction insoluble in acetic-nitric reagent was a small part of the total glucans; however, in the boron-sufficient fibers, there was significantly more of this fraction than in fibers from boron-deficient ovule cultures. The hot water-soluble glucose polymers from the labeled fibers had a significant fraction of the total I''Ciglucose incorporated from UDP-1'4Clglucose. Both f8-1,4-and 8-1,3-water-soluble polymers were formed in the boron-sufricient fibers, whereas the same water-soluble fraction from the boron-deficient fibers was predominantly 8-1,3-polymers. The incorporation of 114CIglucose from GDP-1'4Clglucose by the fibers attached to the ovules was insignificant. One of boron's possible roles in higher plant growth and development is that of regulating metabolic processes that result in the build-up of specific products, including UDP-glucose, glucose-1-P, or 6-P-gluconate (13-15, 22, 23, 34). If boron does play such a regulatory role, it would have some influence on cell wall metabolism including the biosynthesis of cellulose and pectin compounds. Torssell (44) proposed that the "complexes between boric acid and carbohydrates control the deposition of oriented cellulose micells and the accompanying stiffening of the cell wall." Spurr (39) observed that boron deficiency in celery plants did alter plant cell walls, and concluded that boron apparently affects the rate and process of carbohydrate condensation into wall materials. Odhnoff (26) also proposed that boron's influence on bean root cell elongation was probably related to the deposition of new cellulose microfibrils. Whittington (50) suggested that cessation of cell division in boron-deficient field bean radicles was related to abnormalities in cell wall formation which, in turn, prevented the cell wall from becoming organized for mitosis. Later work in the same laboratory (36) revealed that 1[4Ciglucose was incorporated into pectic substances of boron-deficient field bean radicles at a higher level than in boron-sufficient radicles. The authors proposed that boron's role in plant growth is as a bonding agent between cell wall polysaccharides. Wilson (51) also observed that boron deficiency affected cell walls of tobacco pith parenchyma grown in tissue culture by doubling the amount of cell wall fraction with no apparent change of the cellulose: pectic substance ratio as compared to control grown tissue. Boron enhanced the incorporation of myo-[3H]inositol into L-arabinosyl units from pectin of pea...

Synthesis, Salvage, and Catabolism of Uridine Nucleotides in Boron-Deficient Squash Roots

“…Dugger and co-workers (5, 10, 36) have provided evidence that boron deprivation results in reduced UDP-glucose formation. This would result in reduced sucrose synthesis (10), increased starch formation (11), and interference with normal cell wall formation (12,17,18,(33)(34)(35) to an impairment of the utilization of uridine nucleotides for the synthesis of cytidine or thymidine nucleotides or an alteration in the interconversion of nucleotides for the provision of adequate levels of pyrimidine mono-, di-, and triphosphates remains to be examined.…”

Incorporation of UDPGlucose into Cell Wall Glucans and Lipids by Intact Cotton Fibers

“…,8-l1,4-Linked acetic-nitric reagent soluble glucans make up a small fraction of the total soluble glucans, as previously shown (9); however, the majority of the soluble ['4C]glucans were #-l1,3-linked glucans (Fig. 2, A and B) (3,(6)(7)(8)(9).…”

“…With cotton fibers grown in vitro, where there was no restricting cutin or suberin layer, UDPglucose can be incorporated by these intact cells as shown in Figure 1; this incorporation was biphasic, showing Vm,, and Km values somewhat similar to those reported for glucan synthase I and II. ,8-l1,4-Linked acetic-nitric reagent soluble glucans make up a small fraction of the total soluble glucans, as previously shown (9); however, the majority of the soluble ['4C]glucans were #-l1,3-linked glucans (Fig. 2, A and B) (3,(6)(7)(8)(9).…”

“…These intact fibers also rapidly synthesize neutral and polar glucolipids. This work indicates that the plasma membrane-cell wall interfacial region of in vitrogrown cotton fibers are fully capable of utilizing externallysupplied UDPglucose and to partially mimic the synthetic processes observed when labeled substrates, that will penetrate the plasma membrane, are used to investigate cell wall glucan synthesis by intact tissue (3,10,25).…”

“…(t) Intact tissue or unaltered cell membranes are impermeable to UDPglucose and will not incorporate this externally supplied substrate into ,8-1,4-linked glucans (3,4,6,29 (3,30). This reagent will, however, solubilize some ,-1,4-glucans (7,9). In all cases, the linkage of the synthesized glucans need to be confirmed by methylation analysis (3,4,7,16).…”