Buds

The selective death of buds and apices determines branching patterns, life form and anuuality/perenniality. A bud is a compressed system of axis and laterals invested in cataphylls, and progressive acropetal senescence may work its way up to the meristematic region itself, resulting in developmental arrest and ultimately loss of viability (Ofir et al. 1967, Bleecker and Patterson 1997). Apical senescence has been intensively studied in peas. In this species the apical bud is sensitive to a number of developmental and chemical signals, including flowering (Reid 1980), fruiting (Lockhart and Gottschall 1961), gibberellin (Wang et al. 2007), auxin (Zhu and Davies 1997) and calcium (Li et al. 2004). A number of genetic variants have been described differing in sensitivity and execution of the syndrome of apical bud senescence (Marx 1983) and senescence has been modified by transgenic manipulation of gibberellin-sensitive genes (Wang et al. 2004).

Post-harvest deterioration in brassicas such as broccoli, brussels sprouts and cabbage represents an economically significant example of bud senescence. Zhuang et al (1995) stated that senescence-associated chemical changes in the buds and florets of broccoli heads post-harvest were closely related. A number of studies have identified senescence-associated genes and gene products in broccoli and other brassics that match the profile of expression in leaves (Wang et al. 2004, Page et al. 2001, Coupe et al 2003, Satoh et al. 2001, Solymosi et al. 2004).

References

• Bleecker AB, Patterson SE (1997) Last exit: senescence, abscission, and meristem arrest in Arabidopsis. Plant Cell 9, 1169-1179.
• Coupe SA, Watson LM, Ryan DJ, Pinkney TT, Eason JR (2003) Molecular analysis of programmed cell death during senescence in Arabidopsis thaliana and Brassica oleracea: cloning broccoli LSD1, Bax inhibitor and serine palmitoyltransferase homologues. Journal of Experimental Botany 55: 59-68.
• Li J, Wang DY, Li Q, Xu YJ, Cui KM, Zhu YX (2004) PPF1 inhibits programmed cell death in apical meristems of both G2 pea and transgenic Arabidopsis plants possibly by delaying cytosolic Ca2+ elevation. Cell Calcium 35: 71-77.
• Lockhart JA; Gottschall V(1961) Fruit-induced and apical senescence in Pisum sativum L. Plant Physiology 36: 389–398.
• Marx GA (1983) Developmental mutants in some annual seed plants. Annual Review of Plant Physiology 34: 389-417.
• Ofir M, Koller D, Negbi M (1967) Studies on the physiology of regeneration buds of Hordeum bulbosum. Botanical Gazette 128: 25-34.
• Page T, Griffiths G, Buchanan-Wollaston? V (2001) Molecular and biochemical characterization of postharvest senescence in broccoli. Plant Physiology 125: 718–727.
• Reid JB (1980) Apical senescence in Pisum: A direct or indirect role for the flowering genes? Annals of Botany 45: 195-201.
• Satoh H, Uchida A, Nakayama K, Okada M (2001) Water-soluble chlorophyll protein in Brassicaceae plants is a stress-induced chlorophyll-binding protein. Plant Cell Physiology 42: 906-911.
• Solymosi K, Martinez K, Kristóf Z, Sundqvist C, Böddi B (2004) Plastid differentiation and chlorophyll biosynthesis in different leaf layers of white cabbage (Brassica oleracea cv. capitata). Physiologia Plantarum 121: 520–529.
• Wang D-Y, Li Q, Cui K-M, Zhu Y-X (2007) Gibberellin Is Involved in the Regulation of Cell Death-mediated Apical Senescence in G2 Pea. Journal of Integrative Plant Biology 49: 1627–1633.
• Wang YT, Yang CY, Chen Y-T, Lin Y, Shaw J-F (2004) Characterization of senescence-associated proteases in postharvest broccoli florets. Plant Physiology and Biochemistry 42: 663-670.
• Zhuang H, Hildebrand DF, Barth M (1995) Senescence of broccoli buds is related to changes in lipid peroxidation. Journal of Agricultural and Food Chemistry 43: 2585-2591.
• Zhu YX, Davies PJ (1997) The control of apical bud growth and senescence by auxin and gibberellin in genetic lines of peas. Plant Physiology 113: 631–637.