Zeatin: The 60th anniversary of its identification

Abstract

While various labs had shown cell division-inducing activity in a variety of plant extracts for over a decade, the identification of zeatin (Z) in 1964, the first known naturally occurring cytokinin, belongs to Letham and co-workers. Using extracts from maize (Zea mays), they were the first to obtain crystals of pure Z and in sufficient quantity for structural determination by MS, NMR, chromatography, and mixed melting point analysis. This group also crystallised Z-9-riboside (ZR) from coconut (Cocos nucifera) milk. However, their chemical contributions go well beyond the identification of Z and ZR and include two unambiguous syntheses of trans-Z (to establish stereochemistry), the synthesis of 3H-cytokinins that facilitated metabolic studies, and the synthesis of deuterated internal standards for accurate mass spectral quantification. Letham and associates also unequivocally identified Z nucleotide, the 7-and 9-glucoside conjugates of Z, and the O-glucosides of Z, ZR, dihydro Z (DHZ) and DHZR as endogenous compounds and as metabolites of exogenous Z. Their contributions to the role of cytokinins in plant physiology and development were also substantial, especially the role of cytokinins moving in the xylem. These biological advances are described and briefly related to the genetic/molecular biological contributions of others that established that plants have an absolute requirement for cytokinin.

In vitro germination and micropropagation of the Balkan endemic Lilium chalcedonicum L., a potential ornamental lily

“…The effects of BA at 0.2 or 0.5 mg L -1 , with or without the addition of NAA (1 or 0.05 mg L -1 ) were assessed. Moreover, the use of the naturally occurring cytokinin, zeatin, was also evaluated at a concentration of 0.5 mg L -1 in combination with 0.05 mg L -1 NAA (He et al, 2020;Jameson, 2023). In vitro cultures were carried out in glass vessels with a metal cap (7.2 cm × 7.2 cm × 10 cm), with four explants per vessel.…”

A review on mechanisms and prospects of endophytic bacteria in biocontrol of plant pathogenic fungi and their plant growth-promoting activities

“…Endophytic bacteria can also produce cytokinins and gibberellins [ [84] , [171] , [175] ]. Cytokinins regulate cell division, seed germination, elongation of the root, differentiation of chloroplast and xylem, axillary and flowering bud growth, fruit set, leaf senescence, and increase biotic and abiotic tolerance [ [176] , [177] , [178] , [179] , [180] , [181] ]. The root inoculation of P. flourescens strain G20–18, which can produce cytokinins, promoted tomato growth and increased drought tolerance [ 182 ].…”

Cytokinin Translocation to, and Biosynthesis and Metabolism within, Cereal and Legume Seeds: Looking Back to Inform the Future

“…Zeatin was identified from Zea mays seeds by Letham and colleagues in 1964 [6]. The review 'Zeatin: the 60th anniversary of its identification' [7] did not include a detailed exposition of early research into the translocation of cytokinins to and within pods and seeds, or the metabolism of cytokinins during seed development. This review considers these aspects and introduces more recent work as it validates, or not, the conclusions from what was the era of biochemical analyses of legumes and cereals.…”

“…During the 1950s and early 1960s, multiple laboratories were actively working to identify naturally occurring cell-division-inducing factors [7]. Early research by Letham drew positive correlations between cell-division-inducing factors in bioassays and cell division in apple [16] and plum fruitlets [17]; both cell-division-inducing factors were likely to be trans-zeatin (tZ).…”