Donald L. Brummett

Leaf age, decline in photosynthesis, and changes in abscisic acid, indole-3-acetic acid, and cytokinin in cotton leaves

Abstract Abscisic acid (ABA) decreases stomatal aperture and has been reported to decrease photosynthesis. Conversely, indole-3-acetic acid (IAA) and cytokinins have been reported to increase stomatal aperture and stimulate photosynthesis. Field experiments were conducted in 1990 and 1991 to determine possible correlations of concentrations of ABA, IAA, and the cytokinin, isopentenyladenosine ([9R]iP), with a decline in photosynthesis that occurs in cotton (Gossypium hirsutum L.) leaves as they age. Sympodial leaves were tagged 31 July 1990 at the first node of fruiting branches when the flower was at anthesis at that node. Photosynthesis was measured at intervals thereafter during the next 37 days as the tagged leaves became older. Mainstem leaves were selected at 4, 8, 12 and 16 nodes below the apex on 7 August 1991. Photosynthesis rates were determined in full sunlight and the leaves then harvested and analyzed for free and conjugated ABA, free and ester IAA, and the cytokinin, [9R]iP. Free ABA decreased, rather than increased, with leaf age. Although conjugated ABA increased with leaf age, it is though to be sequestered in vacuoles and, therefore, metabolically inaccessible. [9R]iP changed little with leaf age. Ester IAA increased with leaf age and was negatively correlated with photosynthesis. Free IAA decreased with leaf age and was significantly correlated with photosynthesis.

Solid-phase extraction of cytokinins from aqueous solutions with C18 cartridges and their use in a rapid purification procedure.

Eleven cytokinins-including bases, ribosides, glucosides, and ribotides-were tested for their retention on C18 cartridges that were washed with 40 mL of water or a dilute acid at pH 3. Cytokinins were then eluted with methanol and analyzed by high performance liquid chromatography (HPLC). All pure cytokinin were well retained when the cartridge was washed with water, but Z and (diH)Z were less well retained at pH 3. The ribotides required 80% methanol for elution. Cotton leaf tissue (500 mg dry wt) was spiked with cytokinins, extracted with 80% methanol, and the extract bulk purified with hexane, insoluble polyvinylpyrrolidone, and minicolumns (strong anion exchange, amino, and C18 cartridges). Ribotides, added to leaf tissue, could not be recovered as ribotides; it was necessary to hydrolyze and purify them as ribosides. The cytokinins were separated and analyzed by HPLC on strong cation exchange and C18 columns. Recoveries through the entire procedure averaged 70%.

Fruiting of cotton IV. Nitrogen, abscisic acid, indole-3-acetic acid, and cutout

Abstract Decreases in growth, flowering rate, and fruit (boll) retention of cotton ( Gossypium hirsutum L.) characterize cutout, a hiatus in fruiting. Nitrogen deficiency hastens cutout, and has been reported to cause an increase in the concentration of abscisic acid (ABA), a growth-inhibiting hormone. A field experiment was conducted with ‘Deltapine 61’ cotton to determine possible effects of N deficit on the concentrations of ABA and the growth-promoting hormone, indole-3-acetic acid (IAA), in cotton fruiting branches in relation to their growth, flowering rate, and boll retention. Three harvests were made during the fruiting cycle in 1987 to determine if the ABA concentration of fruiting branches increased or IAA concentration decreased as growth decreased during the season. Three harvests were made the next season (1988) to determine possible changes in concentrations of ABA and IAA in flower buds and flowers. Fruiting branches were always shorter on low-N than on high-N plants, and fruiting branches that developed late in the season were much shorter than those that developed early. The ABA concentrations in fruiting branches decreased after 9 July and ABA concentrations were always lower in fruiting branches of low-N than high-N plants. Therefore, the results do not support the hypothesis that ABA accumulates in N-deficient cotton fruiting branches and inhibits their growth. Decreasing concentrations of IAA, however, could have been a cause of decreased growth of fruiting branches. The IAA content of fruiting branches decreased during the fruiting cycle, and was lower in low-N than in high-N plants except in the last harvest. ABA increased and IAA decreased in 3-day-old bolls as boll retention decreased. The concentrations of ABA in flower buds and flowers did not increase during the season and were not affected by N deficiency. Likewise, the concentrations of IAA in flower buds and flowers were not affected by N. The concentration of IAA in flower buds decreased during the season, however. In general, the results support the hypothesis that the IAA of cotton fruiting branches is affected by N deficit, decreases during the fruiting cycle, and may be a factor in the decreases in growth, flowering, and boll retention commonly referred to as cutout.

Influence of defruiting on the abscisic acid and indole-3-acetic acid contents of cotton leaves

A field experiment was conducted to test the hypothesis that young cotton (Gossypium hirsutum L.) fruits (bolls) serve as sinks for ABA, or that they are a source of IAA for subtending leaves. Cotton was grown in eight four-row plots in Phoenix during the summer of 1989 and irrigated about every two weeks. In one test, flowers at anthesis were removed on 22 and 29 June and on 7 and 14 July from the first node of fruiting branches of one center row, but not the other row, in each of four replications. Subtending leaves were harvested seven days after deflowering for ABA and IAA analyses. Removal of one flower per plant had no consistent effect on the concentrations of ABA and IAA in the subtending leaf. In another test, all flowers and bolls were removed from all plants of one center row, but not the other row, of four replications on 30 June and 5 and 13 July. Uppermost fully expanded mainstem leaves were harvested from the same plots on 20, 25, and 27 July, and on 9 August (7, 12, 14, and 27 days after final defruiting) for ABA and IAA analyses. Removal of all fruits apparently caused a slight increase in ABA concentration in mainstem leaves, but the effect disappeared with time after defruiting. The ability of leaves to accumulate ABA apparently decreased slightly as boll load increased. Complete fruit removal did not, however, affect the IAA content of leaves.