Underground gibberellin activity: differential gibberellin response in tomato shoots and roots

SummaryGibberellins (GAs) are growth-promoting hormones that regulate organ growth, mainly via cell elongation. Contradicting reports leave an open question of whether GA is as important for root elongation as it is for stem elongation.Here we have addressed this question focusing on tomato (Solanum lycopersicum) primary-root elongation. We used a combination of physiological, molecular and genetic approaches to tackle this question.Tomato has three GA receptors; GID1a, GID1b1 and GID1b2. The loss of all three receptors, strongly suppressed stem elongation and leaf expansion, but had a relatively minor effect on primary root elongation. The effect of GA on cell elongation and gene-expression was much weaker in roots, than in shoots, reaching saturation at lower hormone concentrations. Our results imply that this differential response to GA in shoots and roots is caused by the lower expression of the dominant GA receptor GID1a in roots.We show that the differential activity of GA between shoots and roots affects root-to-shoot ratio, and speculate that this evolved as an adaptive mechanism to changing environments.

Mutations in the tomato gibberellin receptors suppresses xylem proliferation and reduces water loss under water-deficit conditions

Low gibberellin (GA) activity in tomato (Solanum lycopersicum) inhibits leaf expansion and reduces stomatal conductance. These lead to lower transpiration and improve water status under transient drought conditions. Tomato has three GIBBERELLIN-INSENSITIVE DWARF1 (GID1) GA receptors with overlapping activities and high redundancy. We have tested whether mutation in a single GID1 reduces transpiration without affecting growth and productivity. CRISPR-Cas9 gid1 mutants were able to maintain higher leaf water content under water-deficit conditions. Moreover, while gid1a exhibited normal growth, it showed reduced whole plant transpiration and better recovery from dehydration. Mutation in GID1a inhibited xylem vessels proliferation that led to lower hydraulic conductance. In stronger GA mutants, we also found reduced xylem vessel expansion. These results suggest that low GA activity affects transpiration by multiple mechanisms; it reduces leaf area, promotes stomatal closure and reduces xylem proliferation and expansion and as a result, xylem hydraulic conductance. We further examined if gid1a perform better than the control M82 in the field. Under these conditions, the high redundancy of GID1s was lost and gid1a plants were semi-dwarf, but their productivity was not affected. Although gid1a did not perform better under drought conditions in the field, it exhibited higher harvest index.HighlightThe loss of the tomato gibberellin receptors GID1s reduced xylem proliferation and xylem hydraulic conductance. These contribute to the effect of low gibberellin activity on water loss under water-deficit condition.

Response of Plant Hormone bioassay to Paclobutrazol

Quantitative estimation of a known or suspected biologically active substance (such as a hormone or drug) by measuring its effect on a living organism in standard conditions is known as bioassay. The interaction of gibberellic acid (GA3) and paclobutrazol (PBZ) in lettuce hypocotyl bioassay and 6-benzyl aminopurine (BAP) and paclobutrazol in radish cotyledon enlargement test that paclobutrazol counteracts gibberellin activity when applied exogenously. The radish cotyledon enlargement at low concentration without counteracting BAP action. The reduction of growth to be counteracting of gibberellin activity by paclobutrazol as well as its cytokinin well activity at lower concentration which indicate concentration of gibberellins activity as evidence by their respective bioassay in the present investigation. Paclobutrazol slightly increased radish cotyledon growth at low concentration (up to 0.01 ppm) and could not counteract the growth caused by 1.0 ppm BAP at its 0.001 to 1.0 ppm concentrations suggesting independent effect of paclobutrazol to that of BAP. Furthermore, the activity of paclobutrazol was tested in corn root curvature test and it was found that PBZ concentrations from 0.001 to 10.0 ppm linearly increased the percentage of corn roots showing more than 90° curvature. Therefore, suggession that PBZ conutracted GA3, induced growih and also as IAA and cytokinin at lower concentration0.001 to 100ppm.

Effects of plant growth regulators on the in vitro flowering of carnation (Dianthus caryophyllus L.)

The flowering of terminal shoot of carnation has three stages: inflorescence, floral initiation and blooming. Respiration rate increased in the transition from the vegetative growth to the flowering and all the stages of flowering had high respiration rate. Auxin and gibberellin activities, the proportion of auxin to cytokinin increased, and the elongation of inflorescence stem began in the transition from the vegetative growth to floral initiation stage are involved. Auxin and cytokinin activity increased, the proportion of auxin to cytokinin and gibberellin activity decreased in the transition from the floral initiation to blooming stage. Most vegetative shoots became floral buds by two ways: one way induced by auxin with 0.25 mg/LIAA, and the other by cytokinin with 0.25 mg/L BA.

Changes in endogenous gibberellin-like substances in onion bulbs (Allium cepa L.) cv. Sochaczewska during storage

Onions cv. Sochaczewska were dried up under an umbrella roof till October 15th or till November 15th and thereafter stored in a cold room at 0-1°C until May 15th. During 4-year of experiment gibberellin activity was determined each month during storage. Three periods of high activity of gibberellins were found in most cases: in December, in February-March and in late spring. In general, onions dried longer (till November 15th), showed lower gibberellin activity than onions dried shorter. Gibberellin-like substances under investigation are localized in almost all Rf zones of chromatogram. Sprouting and rooting was related to gibberellin activity.