Gibberellins and Heterosis in Maize

Abstract

Under controlled environment and/or fIed conditios, vegetative growth (height, internode length, leaf area, shoot dry weight, grain yield) was greater in an F1 maize hybrid than in either parental Inbred. Endogenous gibberelin (GA)-llke substances in apical meristem cylinders were also higher in the hybrid than in either Inbred, both on a per plnt and per gram dry weight basis. There were no apparent qualitative differences in GAUlke substances, however. Levels of GA-Rke substances in all genotypes were highest prior to tassel initiation. Chromatographic comparisons of the GA-Se substances and authentic standards of GA native to maize on gradient-eluted SK0 partiton and reverse-phase C1i high-pressure liquid chromatography columns are described. No consistent differences in abscisic acid levels of the three genotypes were observed. This correlation of heterosis for endogenous GA-lie substances with heterosis for growth suggests that amounts of endogenous GA may be related to hybrid vigor in maize.Hybrid vigor, the phenotype of heterosis, exists when hybrid performance exceeds that of the parental genotypes. Hybrid vigor is repeatedly observed for growth, yield, and even certain developmental characters of maize (19,20,23). Indeed, the impressive increases in yield of maize during the 20th century have largely resulted from the increased use of hybrid seed (6, 7). However, while plant breeders and agronomists have been utilizing heterosis as a means of improving crop productivity, the physiological basis of heterosis is not presently understood (23).The involvement of plant hormones in heterosis is both an attractive and logical possibility. Changes in endogenous hormone balance could amplify genotypic differences, thus leading to major phenotypic effects. Although the possibility of hormonal involvement in heterosis has been suggested previously (14), Sinha and Khanna (23) note that no correlative relationships between endogenous hormone levels and hybrid vigor had been described prior to 1975. We are unaware of any subsequent reports of such correlative relationships.In a previous study (17), it was observed that growth rate and content of endogenous two maize inbreds and their F1 hybrid grown under two lowtemperature regimes with dominance for increased growth rate being observed in the hybrid grown under the low-temperature conditions (17). Apparent 'overdominance' (inasmuch as it is difficult to separate overdominance per se from complementation, overdominance will be used in this paper) had been repeatedly observed when the same maize genotypes were grown under warmer growth cabinet or field conditions (20). Thus, the next logical question to be addressed was: under favorable temperature conditions are growth rates and levels of endogenous GA-like substances still correlated; does heterosis for increased levels of GA-like substances accompany heterosis for growth rate? The present study was initiated to investigate this question. Additionally, because ABA is sometimes assigned an inhibitory role i...

Heterosis: Many Genes, Many Mechanisms—End the Search for an Undiscovered Unifying Theory

“…In maize, inbreds contain less endogenous GA and precursors than corresponding hybrids [52]. Application of exogenous GA stimulates growth of inbreds more than hybrids [53,54], consistent with the hypothesis that the reduced efficiency of inbreds to produce GA results in reduced biomass accumulation. A recent study in rice provides similar support for the role of GA in heterosis for biomass accumulation [55].…”

Gibberellins: A Phytohormonal Basis for Heterosis in Maize

“…Systemic changes during inflammation such as increased acute-phase protein synthesis and fever probably represent action of these cytokines on liver and hypothalamus. Interleukin-i (IL-1) and tumor necrosis factor-a (TNF-a) were the first monocyte-derived cytokines shown to properties in immunity and inflammation (3,4).…”

“…The correlation between inbreeding and the responsiveness to exogenous GA3 suggests that the growth of inbreds is limited by a deficiency of endogenous GAs. (ii) The endogenous GA-like substances have been quantified by bioassay from two inbreds and their heterotic hybrid (3), and significantly higher concentrations of GA-like activity were observed in the hybrid over a sequence of harvests (3). (iii) Heterosis for early seedling growth of maize is frequently observed (4,5), and the rapid production ofhydrolytic enzymes such as aamylase and protease is essential to provide respiratory substrates for this heterosis of early seedling growth (4,6).…”

Phytohormonal Regulation of Biomass Allocation and Morphological and Physiological Traits of Leaves in Response to Environmental Changes in Polygonum cuspidatum

“…Gibberellins (GAs) may be involved also in regulating biomass allocation and LMA in addition to their well-known roles in stem and petiole elongation, seed germination, and flowering (Hedden and Thomas, 2012 ). Genotypes with high levels of endogenous GAs show high L / R or shoot-to-root ratios and low LMA compared to those with low levels of endogenous GAs in Zea mays (Rood et al, 1983 ), Populus sp. (Bate et al, 1988 ), Plantago major (Dijkstra et al, 1990 ), Brassica rapa (Rood et al, 1990 ), and Solanum lycopersicum (Nagel et al, 2001a ).…”