Table 1.

Stamen-related features of GA deficient mutants. ent-copalyl diphosphate synthase (CPS); ent-kaurene acid oxidase (KAO); GA 20-oxidase (GA20ox); GA 3-oxidase (GA3ox); reduced pollen elongation1 (rpe1); pollen mother cells (PMCs).

Gene	Mutant	Phenotype	Species	Refs
AtCPS	ga1-3	Male-sterile phenotype, which can be reversed by GA application	Arabidopsis	[40]
		Anther and pollen development is blocked after meiosis but prior to mitosis
		Pollen sacs expansion arrest
		Inability to release microspores
		Tapetum remains at the vacuolated stage and degenerates together with the microspores
		Inhibition of filament elongation by a reduction of the length, not the number of cells
		Altered ratio of stamen-pistil length in the flowers of mature mutant
LeCPS	gib-1	Initiation of floral meristems and development of all floral organs proceeds normally up to a certain point, but then normal development ceases and flower buds eventually abort	tomato	[47]
		Microsporogenesis is blocked before meiosis
		Anthers of developmentally arrested buds contain PMCs that are in the G1 phase of premeiotic interphase. Following treatment of mutant buds with GA3, premeiotic DNA synthesis and callose accumulation in PMCs are evident by 48 h posttreatment, and within 66 h, prophase I of meiosis and meiosis-related changes in tapetum development are observable
OsCPS1	oscps1-1	One of the most severe GA-deficient mutant	rice	[48]
		GA treatment rescues the defect in stamen development
		Abnormal enlargement of tapetal cells, to the point of almost filling the locule space
		Collapse of microspores
LeKAO	ga-2	Flower buds are initiated, but do not develop to maturity and eventually abort	tomato	[39]
		Cells of the sporogenous layer are initiated, but growth is arrested and cells eventually degenerate
		Inhibition of microsporogenesis occurs before meiosis
		Stamen do not elongate
OsKAO	rpe1	Intermediate severity GA-deficient mutant	rice	[49]
		The mutant develops typical flowers with normal pistils and stamens
		Pollen viability and the number of mature pollen grains in mutant are similar to those of the WT plant
		Impaired pollen germination and elongation
GA20ox	ga20ox1 ga20ox2	Semidwarf, semifertile phenotype, with early flowers failing to set seed	Arabidopsis	[37]
		Self-rescue of seed set occurs in later flowers, although the mechanism remains undetermined
		Normal tapetum degradation
		Fully viable pollen
		Delayed or inhibited anther dehiscence
		Disturbance of filament elongation
	ga20ox1 ga20ox2 ga20ox3-1	For many phenotypic characters, the triple mutant is not significantly different from the ga1-3		[53]
		Postmeiotic arrest in stamen development
		Defect in tapetum degeneration. Tapetum layer fails to degenerate completely and remains in anther locules
		Inhibited anther dehiscence
		Do not undergo late-stage stamen acceleration, with growth and development instead halting
		Shorter stamens at flower opening
GA3ox	ga3ox1 ga3ox3	The epidermal layer of the anther remains intact, although the tapetum layer disappears, suggesting that anther development is arrested around stages 11 and 12	Arabidopsis	[36]
		Defective pollen after its maturation
		Delayed or inhibited anther dehiscence
		Disturbances in filament elongation
		All defects gradually decrease in the later flowers