The photosynthetic potential of canola embryos

Asokanthan, Ponita S.; Johnson, Robert W.; Griffith, Marilyn; Król, Marianna

doi:10.1034/j.1399-3054.1997.1010215.x

Cited by 29 publications

(41 citation statements)

References 12 publications

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“…Despite the low level of light available inside the seed, the level of photosynthetic activity, as measured by oxygen release, is surprisingly high. This is thought to reflect the specialized nature of chloroplasts present in the seed, whose thylakoids contain chlorophyll–protein complexes similar to leaf chloroplasts, but exhibit a greater proportion of granal stacking (Saito et al ., 1989; Asokanthan et al ., 1997). This adaptation can generate distinct light harvesting properties and low saturation levels for photosynthetic electron transport (Borisjuk et al ., 2005).…”

Section: The Effect Of Environmental Factors On Steady‐state Oxygementioning

confidence: 99%

“…It has been hypothesized that the plastids have become specialized to use light reactions to generate the ATP/NADPH required to fuel biosynthesis of the various storage products. The embryo plastids have been classified as photoheterotrophic organelles (Asokanthan et al ., 1997), which are structurally and metabolically adapted to drive photosynthetic reactions at low light intensities. Thus their activity affects the oxygen status of the seed, determines its energy and redox state and eventually its biosynthetic flux (Browse & Slack, 1985; Ruuska et al ., 2004; Rolletschek & Borisjuk, 2005).…”

Section: The Effect Of Environmental Factors On Steady‐state Oxygementioning

confidence: 99%

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The oxygen status of the developing seed

2009

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SummaryRecent applications of oxygen-sensitive microsensors have demonstrated steep oxygen gradients in developing seeds of various crops. Here, we present an overview on oxygen distribution, major determinants of the oxygen status in the developing seed and implications for seed physiology. The steady-state oxygen concentration in different seed tissues depends on developmental parameters, and is determined to a large extent by environmental factors. Photosynthetic activity of the seed significantly diminishes hypoxic constraints, and can even cause transient, local hyperoxia. Changes in oxygen availability cause rapid adjustments in mitochondrial respiration and global metabolism. We argue that nitric oxide (NO) is a key player in the oxygen balancing process in seeds, avoiding fermentation and anoxia in vivo. Molecular approaches aiming to increase oxygen availability within the seed are discussed.Abbreviations: At, Arabidopsis thaliana; AOX, alternative oxidase; COX, cytochrome C oxidase; HIF1, hypoxia-inducible factor; NO, nitric oxide; ROS, reactive oxygen species. I. IntroductionThe modern atmosphere contains approx. 21 kPa oxygen. However, over the course of the past 550 million yr (Phanerozoic time), during which time the vascular plants invaded the land surface, plants have adapted to levels of atmospheric oxygen ranging from 13 to 51 kPa (Raven, 1991). This variation has been a major driver of plant evolution, and has led to the tuning New Phytologist (2009) 182: 17-30 doi: 10.1111/j. 1469-8137.2008.02752.x Key words: hypoxia, nitric oxide (NO), oxygen diffusion, oxygen sensing, seed development, seed photosynthesis, storage metabolism. Tansley review Review 18New Phytologist ( of plant architecture/ultrastructure and metabolism to tolerate both low and high oxygen supply (Berner, 1999). Although over a shorter time-scale the atmospheric oxygen level may appear stable, plants must be able to adapt to variation in oxygen provision imposed by the local environment. For example, little oxygen is available to the plant root in a temporarily waterlogged soil, so plants have developed a number of strategies for acclimatization, avoidance and escape (Armstrong et al., 1994; Crawford & Brändle, 1996; Drew, 1997;Vartapetian et al., 2008). The diffusion of gas is 10 000 fold slower through a liquid medium than through air, so waterlogging rapidly leads to hypoxic and eventually even to anoxic conditions. Under hypoxia, the concentration of oxygen limits mitochondrial ATP production (oxidative phosphorylation), whereas under anoxia there is essentially no oxygen available for mitochondrial respiration. A restricted capacity for oxygen diffusion, in conjunction with a high rate of cellular metabolism, can generate hypoxia even in aerial organs such as the fruit (Ke et al., 1995), certain vascular tissues (Kimmers & Stringer, 1988), the pollen grain (Leprince & Hoekstra, 1998) and the seed (Rolletschek et al., 2002). From a historical perspective, seed germination and subsequent seedling growth has been one of...

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Section: The Effect Of Environmental Factors On Steady‐state Oxygementioning

confidence: 99%

Section: The Effect Of Environmental Factors On Steady‐state Oxygementioning

confidence: 99%

The oxygen status of the developing seed

2009

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“…In Brms-ica napus, approximately 30% of incident light is transmitted through the silique wall, suggesting that c. 1500 pnol.m-2.sec-' external PAR would be required for light compensation point in the chlorophyllous embryos (Eastmond et al, 1996). In this species, although very little carbon is fixed by embryo chloroplasts, significant electron transport has been detected (Asokanthan et al, 1997). It seems likely then that the photoheterotrophic embryos may use the light reactions to generate the ATP and NADPH required to fuel the conversion of maternally supplied sucrose to the fatty acids used in oil synthesis and storage (Asokanthan et al, 1997).…”

Section: Embryo Colourmentioning

confidence: 95%

“…In this species, although very little carbon is fixed by embryo chloroplasts, significant electron transport has been detected (Asokanthan et al, 1997). It seems likely then that the photoheterotrophic embryos may use the light reactions to generate the ATP and NADPH required to fuel the conversion of maternally supplied sucrose to the fatty acids used in oil synthesis and storage (Asokanthan et al, 1997). In canola this seems highly plausible since the seeds are rich in oils; indeed, they have been selectively bred for this trait.…”

Section: Embryo Colourmentioning

confidence: 99%

A survey of seed and seedling characters in 1744 Australian dicotyledon species: cross-species trait correlations and correlated trait-shifts within evolutionary lineages

Wright

Clifford

Kidson

et al. 2000

Biological Journal of the Linnean Society

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Seedling traits have been described across 1744 species of Australian plants. Six traits were coded as binary alternatives: (1) phanerocotyly vs cryptocotyly; (2) first leaf scale-like vs leaflike; (3) first leafsingle vs paired; (4) cotyledons hairy vs. glabrous; (5) hypocotyl hairy vs glabrous, and (6) embryo green vs non-green at maturity. Seed volume was calculated from measurements of seed dimensions. Three approaches were used in analysing the data: (1) the taxonomic distribution of binary character states was described; (2) the strength of bivariate character associations was quantified at species level ('cross-species' correlations and regressions); (3) the data were arrayed on a phylogenetic tree in order to analyse by 'phylogenetic regression' for correlated evolutionary shifts in trait pairs. All the traits appeared evolutionarily malleable. For example, while cryptocotyly was the minority condition (22% of species), it occurred in many different taxa (124 genera, 40 families, 24 orders) with high levels of polymorphy (ISYO, 25% and 42% for genera, families and orders). Similarly, the less common attribute states for first leaf type, hypocotyl texture, cotyledon texture and embryo colour occurred in species from right across the dicotyledon phylogeny, as did independent evolutionary divergences in each of these characters. These patterns indicate that debate over which conditions are primitive and which are advanced will not have any general answer, only an answer for a specific branch-step in the phylogenetic tree. In nearly all cases, correlated-divergence analyses showed the same patterns as cross-species analyses. The strongest associations were between seed volume and cryptocotyIy, seed volume and scale-like first leaf, and seed volume and presence of green embryo. In addition, cryptocotyly and scale-like first leaf, and cotyledon and hypocotyl type, were strongly associated in both correlated-divergence and cross-species analyses. Interpretation of results was mostly presented with respect to seed size, a trait which we consider to be pivotal inaspecies' seedling establishment strategy. All possible pairwisecombinationsofbinary seedling traits were found in our study species. Taken together, the various lines of evidence presented here suggest that the traits have assorted more or less independently of each other and provide no evidence of functional groups based an these attributes. Thus, the several existing seedling typologies should be regarded as classifications of convenience rather than as reflecting fundamental types.

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“…Although changes in embryo development are thought to be triggered by changes in water content, the relative water content declines at a constant rate throughout the development of canola seeds in vivo (Fig. We hypothesize that the embryos are photoheterotrophic and utilize energy derived from the light reactions of photosynthesis to fuel the synthesis of storage compounds from maternally supplied sucrose (Asokanthan et al 1997). In contrast, the Chi content of canola seeds begins to decrease 32 days after pollination (Fig.…”

Section: Embryo Growth In Vivo Vs In Vitromentioning

confidence: 99%

Water and sucrose regulate canola embryo development

Johnson¹,

Asokanthan²,

Griffith³

1997

Physiol Plant

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M. 1997. Water and sucrose regulate canola embryo development. -Physiol. Plant. 101: 361-366.The effect of water and sucrose on the growth and development of zygotic, 30-day-old canola {Brassica napus L. cv. Bounty) embryos was examined in vitro by manipulating the levels of sucrose and/or sorbitol present in the culture medium. In some experiments, the medium water potential was allowed to vary with sucrose concentration, while in other experiments, the medium water potential was held constant by adding sorbitol to varying amounts of sucrose. Our results showed that embryos cultured on sorbitol alone exhibited two developmental patterns: embryos germinated precociously on media containing up to 0.70 M sorbitol, whereas embryos became yellow and quiescent on media with higher concentrations of sorbitol. For embryos cultured on media containing sucrose alone, three distinct developmental patterns were noted: at low sucrose concentrations, embryos germinated precociously; at intermediate concentrations, embryos continued to grow in an embryonic mode; and, at high concentrations, embryos became yellow and quiescent. Continued embryonic growth was never observed in embryos cultured on media containing sorbitol alone. Embryos never germinated precociously when cultured on media maintained at a constant water potential of -1.4 MPa, rather dry weight increased in these embryos with an increase in sucrose concentration. We envision the effect of sucrose on embryo growth and development to be nested within the effect of water availability. When water availability is restricted, embryos become quiescent. When water is available, embryos have the potential to grow, but the developmental growth pattern depends on the availability of sucrose. In the absence of sucrose, embryos germinate and initiate the transition to autotrophy. If sufficient sucrose is available, embryos remain photoheterotrophic and continue to grow in an embryonic mode.

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The photosynthetic potential of canola embryos

Cited by 29 publications

References 12 publications

The oxygen status of the developing seed

The oxygen status of the developing seed

A survey of seed and seedling characters in 1744 Australian dicotyledon species: cross-species trait correlations and correlated trait-shifts within evolutionary lineages

Water and sucrose regulate canola embryo development

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