Not required for normal growth and development of the plant (PubMed:21436043). Involved in defense against lepidopteran, but not coleopteran herbivore insects (PubMed:21436043, PubMed:17416643). Acts in the insect gut to degrade threonine, which is an essential and limiting nutrient for the growth of lepidopteran larvae (Probable). Active against both L-threonine and L-serine (PubMed:17416643). L-threonine = 2-oxobutanoate + NH4(+) L-serine = NH4(+) + pyruvate Threonine dehydratase 2 biosynthetic, chloroplastic: Strongly inhibited by 1 mM isoleucine (PubMed:21436043). Processed threonine dehydratase 2: Not inhibited by isoleucine (PubMed:21436043, PubMed:17416643). Threonine dehydratase 2 biosynthetic, chloroplastic: Active at alkaline pH (PubMed:21436043, PubMed:17416643). Processed threonine dehydratase 2: Optimum pH is 9. Has little or no activity at pH values below 6.0 (PubMed:17416643). Threonine dehydratase 2 biosynthetic, chloroplastic: Optimum temperature is 60 degrees Celsius. Abnormally stable at elevated temperatures (PubMed:21436043). Processed threonine dehydratase 2: Active over a wide range of temperatures. Optimal enzyme activity against L-threonine is at 58 degrees Celsius (PubMed:17416643). Amino-acid biosynthesis; L-isoleucine biosynthesis; 2-oxobutanoate from L-threonine: step 1/1. Homotetramer. Expressed in floral buds, 8-9 mm long flowers 1 to 2 days before anthesis, open flowers and floral organs including sepals, petals, stamens and carpels of 8-9 mm flowers (at protein level) (PubMed:7550377). Expressed in very early floral meristems of the anantha. Over 500-fold expression in mature flowers compared to leaves (PubMed:2011578). Expressed in sepals, petals, stamens and carpels of the mature flower. In sepals, mostly expressed in the abaxial mesophyll cells and in petals in parenchymal cells. Not expressed in epidermal or vascular tissues of sepals and petals. In stamens, expressed in parenchymal cells of the connective and lobes, but not expressed in differentiated tissues such as tapetum (TP), stomium (SM), or pollen grains (PG) (PubMed:2011578, PubMed:7550377). Not expressed in roots or seeds (PubMed:2011578). High level of expression in immature flower buds, unopened flowers and opened flowers (PubMed:17416643, PubMed:7550377). Not expressed in unstressed leaves, root, stem or petiole (PubMed:17416643). During the pre-organogenesis stage of the floral primordium, expressed in scattered islands of cells in the central parenchymatous pith region and in the peripheral ground parenchyma. Upon sepal buttresses emergence, expressed in all parenchyma mesophyll cells accumulating in a continous pattern in the central pith cells of the floral primordia, but not expressed in the future epidermal cells. As the mesophyll and vascular tissues elongate and differentiate, highly expressed in the abaxial mesophyll cells of sepals, but down-regulated in the adaxial cell layers. At anthesis, down-regulated expression in all mesophyll cells of the sepal. In petals, expressed in all mesophyll cells throughout development. Expression is induced in response to methyl jasmonate (MeJA) and locally and systemically in response to mechanical wounding (PubMed:17416643). Parenchyma-specific induction of expression in flowers and leaves by MeJA. No induction of expression by MeJA in epidermal, vascular or sporogenous tissues (PubMed:7550377). Caterpillar (Helicoverpa zea) labial saliva induces expression in leaves damaged by herbivory (PubMed:23065106). Proteolytically cleaved by a chymotrypsin-like digestive protease in the midgut of the lepidopteran insects to remove the C-terminal regulatory domain, which allows efficient metabolizing of threonine in the presence of high isoleucine levels in the gut. Belongs to the serine/threonine dehydratase family.