Metabolic Control of Avocado Fruit Growth (Isoprenoid Growth Regulators and the Reaction Catalyzed by 3-Hydroxy-3-Methylglutaryl Coenzyme A Reductase)

Abstract

The effect of isoprenoid growth regulators on avocado (Persea americana Mill. cv Hass) fruit growth and mesocarp 3-hydroxy-3-methylglutaryl coenzyme A reductase (HMCR) activity was investigated during the course of fruit ontogeny. Both normal and small-fruit phenotypes were used t o probe the interaction between the end products of isoprenoid biosynthesis and the activity of HMCR in the metabolic control of avocado fruit growth. Kinetic analysis of the changes in both cell number and size revealed that growth was limited by cell number in phenotypically small fruit. I n small fruit a 70% reduction i n microsomal HMCR activity was associated with an increased mesocarp abscisic acid (ABA) concentration. Application of mevastatin, a competitive inhibitor of HMCR, reduced the growth of normal fruit and increased mesocarp ABA concentration. These effects were reversed by co-treatment of fruit with mevalonic acid lactone, isopentenyladenine, or N-(2-chloro-4-pyridyI)-N-phenylurea, but were not significantly affected by either gibberellic acid or stigmasterol. However, stigmasterol appeared t o partially restore fruit growth when co-injected with mevastatin i n either phase II or III of fruit growth. I n vivo application of ABA reduced fruit growth and mesocarp HMCR activity and accelerated fruit abscission, effects that were reversed by co-treatment with isopen-tenyladenine. Together, these observations indicate that ABA accumulation down-regulates mesocarp HMCR activity and fruit growth, and that i n situ cytokinin biosynthesis modulates these effects during phase I of fruit ontogeny, whereas both cytokinins and sterols seem to perform this function during the later phases. HMGR catalyzes the irreversible conversion of HMG-COA to MVA, the committed step in isoprenoid biosynthe-sis in all eukaryotic organisms (Goldstein and Brown, 1990). For plant growth and development, synthesis of isoprenoids is fundamental because the pathway supplies compounds that are essential for full morphogenic expression. This class of compounds is of structural significance, e.g. carotenoids and the side chain of chlorophylls and plastoquinone for photosynthesis, the side chain of ubiqui-none for respiration, sterols for membrane structure, and phytoalexins for defense. The pathway also supplies sev

Fruit size QTL analysis of an F1 population derived from a cross between a domesticated sweet cherry cultivar and a wild forest sweet cherry

“…This similar result has also been revealed in other fruit crops such as avocado (Persea americana Mill. ; Cowan et al 1997); melon (Cucumis melo L. reticulatus; Higashi et al 1999), olive (Olea europaea L.; Rapoport et al 2004), peach (Scorza et al 1991), and pear (Zhang et al 2006) by the comparisons among genotypes. However, our analysis failed to identify any QTL for mesocarp cell length despite the significant progeny phenotypic variation and the relatively high broad sense heritability.…”

Terpene production in the peel of sweet orange fruits

“…The expression level of the enzymes was very variable with genes showing up to 49 transcripts (the 1-deoxy-D-xylulose-5-phosphate synthase) and genes showing just one, the hydroxymethylglutaryl-CoA (HMG) reductase. This enzyme is important in the first stages of fruit development (Narita and Gruissem, 1989;Cowan et al, 1997;Kato-Emori et al, 2001;Kobayashi et al, 2002) when it correlates with cell division. In later stages of fruit development, this enzyme does not seem to be active (Narita and Gruissem, 1989;Cowan et al, 1997;Kato-Emori et al, 2001).…”

“…This enzyme is important in the first stages of fruit development (Narita and Gruissem, 1989;Cowan et al, 1997;Kato-Emori et al, 2001;Kobayashi et al, 2002) when it correlates with cell division. In later stages of fruit development, this enzyme does not seem to be active (Narita and Gruissem, 1989;Cowan et al, 1997;Kato-Emori et al, 2001). Also noticeable, 1-deoxy-D-xylulose-5-phosphate synthase (DXPS) was detected as the most expressed gene within the mevalonate-independent pathway.…”

Factores ecofisiológicos relacionados con el crecimiento vegetativo, floración y desarrollo del fruto del aguacate.

“…Por otra parte, tratamientos con manoheptulosa a los frutos aumentan la actividad de la enzima HMGR (3-hydroxy-3-methyl-glutaryl coenzima A reductasa) en los tejidos de la semilla entre un 19% y un 45% (Cowan, 2004). La HMGR es una enzima clave relacionada con la síntesis de compuestos isoprenoides, relacionados con estructuras tales como los carotenoides, clorofilas, plastoquinona (fotosíntesis), esteroles, fitoalexinas y varias sustancias reguladoras del desarrollo, que incluyen el ácido abscísico, brasinosteroides, giberelinas y citoquininas (Cowan et al, 1997), por lo que contribuye a un control, tanto temporal como espacial, de los eventos durante la ontogenia de las plantas. Cowan (2004) señala que la actividad de la enzima HMGR en los tejidos de la semilla de aguacate, es sensible al H 2 O 2 y sugiere que el perseitol y la manoheptulosa, que están relacionados por oxidación y reducción, eliminarían las ROS que podrían, de otra forma, inactivar la HMGR durante el curso normal del crecimiento del fruto o causar un daño oxidativo.…”

“…Los valores de ФPSII no se vieron modificados por ninguno de los tratamientos, coincidiendo con lo ya visto para el rayado en otoño. Aún cuando este tratamiento de anillado produjo un incremento del diámetro ecuatorial del fruto maduro, 6 meses después del tratamiento, con el transcurso del tiempo esta diferencia se perdió, debido probablemente al hecho de que el fruto del aguacate presenta un comportamiento algo inusual, ya que el crecimiento del mesocarpo por división y expansión celular continúa hasta llegada la madurez del fruto (Cowan et al, 1997), existiendo un crecimiento compensatorio que logra minimizar el efecto inicial sobre el crecimiento de los frutos.…”