Localization of Carbohydrate Metabolizing Enzymes in Guard Cells of <i>Commelina communis</i>

Robinson, Nina L.; Preiss, Jack

doi:10.1104/pp.85.2.360

Cited by 27 publications

(26 citation statements)

References 27 publications

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“…More than 90% of the total amylolytic activity in pea leaves has been reported to be extrachloroplastic (16). Similarily, 70 and 80% of the total amylolytic activity is located in the extrachloroplastic fractions munis guard cells (23) and spinach mesophyll cells (21), respectively. All or most of the total endoamylolytic activity in pea and barley leaves has usually been found to be extraplastidic (13,16,17,25).…”

mentioning

confidence: 67%

Amylases in Pea Tissues with Reduced Chloroplast Density and/or Function

Saeed

Duke²

1990

Plant Physiol.

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Pea (Pisum sativum L.) tissues with reduced chloroplast density (e.g. petals and stems) or function (i.e. senescent leaves and leaves darkened for prolonged periods) were surveyed to determine whether tissues with genetically or environmentally reduced chloroplast density and/or function also have significantly different amylolytic enzyme activities and/or isoform patterns than leaf tissues with totally competent chloroplasts. Native PAGE followed by electrophoretically blotting through a starch or ,B-limit dextrin containing gel and KI/12 staining revealed that the primary amylases in leaves, stems, petals, and roots were the primarily vacuolar fI-amylase (EC 3.2.1.2) and the primarily apoplastic aamylase (EC 3.2.1.1). Among tissues of light grown pea plants, petals contained the highest levels of total amylolytic (primarily Bl-amylase) activity and considerably higher ratios of ,-to aamylase. In aerial tissues there was an inverse relationship between chlorophyll and starch concentration, and fl-amylase activity. In sections of petals and stems there was a pronounced inverse relationship between chlorophyll concentration and the activity of a-amylase. Senescing leaves of pea, as determined by age, and protein and chlorophyll content, contained 3.8-fold (fresh weight basis) and 32-fold (protein basis) higher a-amylase activity than fully mature leaves. Leaves maintained in darkness for 12 days displayed a 14-fold (fresh weight basis) increase in aamylase activity over those grown under continuous light. In senescence and prolonged darkness studies, the a-amylase that was greatly increased in activity was the primarily apoplastic aamylase. These studies indicate that there is a pronounced inverse relationship between chloroplast function and levels of apoplastic a-amylase activity and in some cases an inverse relationship between chloroplast density and/or function and vacuolar 8-amylase activity.The physiological roles of amylases in vegetative tissues of higher plants are poorly understood. One reason for this current state of confusion is that at the cellular level most of the amylolytic activity in plant vegetative tissues is extrachloroplastic, away from the site of starch synthesis and degradation. More than 90% of the total amylolytic activity in pea leaves has been reported to be extrachloroplastic (16).

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confidence: 67%

Amylases in Pea Tissues with Reduced Chloroplast Density and/or Function

Saeed

Duke²

1990

Plant Physiol.

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“…Starch would be converted to sucrose only under blue light by a DCMU-insensitive mechanism requiring chloroplastic Pi (25). This reaction would occur regardless of whether KC1 was present.…”

Section: Resultsmentioning

confidence: 99%

Sugar Concentrations in Guard Cells of Vicia faba Illuminated with Red or Blue Light

Poffenroth¹,

Green²,

Tallman³

1992

Plant Physiol.

103

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Concentrations of soluble sugars in guard cells in detached, sonicated epidermis from Vicia faba leaves were analyzed quantitatively by high performance liquid chromatography to determine the extent to which sugars could contribute to changes in the osmotic potentials of guard cells during stomatal opening. Stomata were illuminated over a period of 4 hours with saturating levels of red or blue light, or a combination of red and blue light. When stomata were irradiated for 3 hours with red light (50 micromoles per square meter per second) in a solution of 5 millimolar KCI and 0.1 millimolar CaC12, stomatal apertures increased a net maximum of 6.7 micrometers and the concentration of total soluble sugar was 289 femtomoles per guard cell (70% sucrose, 30% fructose). In an identical solution, 2. Light-induced stomatal opening is caused by the accumulation of both inorganic and organic solutes in guard cells. There is wide agreement that potassium ions (K+) and malic acid are the major solutes that produce the turgor pressure that drives stomatal opening (8,13,20,23,38). Nevertheless, several lines of evidence suggest that soluble sugars may also be significant as osmotica in guard cells of open stomata. noted that when stomata in detached leaf epidermis of Commelina communis were induced to open with light, rates ofK+ and malate accumulation could not account for all of the osmotica necessary to support the rate of stomatal opening in the early stages when apertures were '10 ,um. Outlaw and Manchester (18) removed epidermis from leaves of Vicia faba in which stomata were either open or closed and showed that stomatal opening to 10 ,m was accompanied by an increase of 420 to 720 fmol of hexose sugars and 140 fmol of sucrose per guard cell. Furthermore, they demonstrated the sugar content of these cells to be inversely proportional to the amount of starch present, although they did not identify whether sugars were produced by degradation of guard cell starch or were from other endogenous or exogenous sources. Based on these results, MacRobbie (12) has suggested that soluble sugars might account for the additional osmoticum necessary to support the rate of stomatal opening observed in Commelina.Experiments with whole leaves (3), detached leaf epidermis (17,27,34), and guard cell protoplasts (1,28,30) suggest that there are two photoreceptor systems in guard cells, one for blue light and the other for red light. Both systems can activate proton extrusion from the guard cell plasma membrane (1,28,30). In solutions containing KCI, blue light-induced stomatal opening in detached epidermis of V. faba saturates at 25 umol m-2 s-', is inhibited completely by KCN, and is inhibited partially by DCMU at intensities 225 umol m-2 s-' (27). In a similar solution, red light-induced opening saturates at 50 ,umol m-2 s-', is insensitive to KCN, and is completely inhibited by DCMU (27). In previous time course experiments (34), qualitative histological analysis of guard cells of www.plantphysiol.org on May 10, 2018 -Published ...

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“…In contrast to the case of cereal endosperms possessing most of AGP in the extraplastidial compartment (56,65,66), AGP locates exclusively in the chloroplast of leaves (67)(68)(69). Thus, it is highly conceivable that some ADPG produced in the plastid is exported to the cytosol before it is imported again to the chloroplast.…”

Section: Extraplastidial Expression Of Aspp Does Not Affect the Phenomentioning

confidence: 98%

Most of ADP·glucose linked to starch biosynthesis occurs outside the chloroplast in source leaves

Baroja‐Fernández

Muñoz

Zandueta-Criado

et al. 2004

Proc. Natl. Acad. Sci. U.S.A.

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Sucrose and starch are end products of two segregated gluconeogenic pathways, and their production takes place in the cytosol and chloroplast of green leaves, respectively. According to this view, the plastidial ADP⅐glucose (ADPG) pyrophosphorylase (AGP) is the sole enzyme catalyzing the synthesis of the starch precursor molecule ADPG. However, a growing body of evidences indicates that starch formation involves the import of cytosolic ADPG to the chloroplast. This evidence is consistent with the idea that synthesis of the ADPG linked to starch biosynthesis takes place in the cytosol by means of sucrose synthase, whereas AGP channels the glucose units derived from the starch breakdown. To test this hypothesis, we first investigated the subcellular localization of ADPG. Toward this end, we constructed transgenic potato plants that expressed the ADPG-cleaving adenosine diphosphate sugar pyrophosphatase (ASPP) from Escherichia coli either in the chloroplast or in the cytosol. Source leaves from plants expressing ASPP in the chloroplast exhibited reduced starch and normal ADPG content as compared with control plants. Most importantly however, leaves from plants expressing ASPP in the cytosol showed a large reduction of the levels of both ADPG and starch, whereas hexose phosphates increased as compared with control plants. No pleiotropic changes in photosynthetic parameters and maximum catalytic activities of enzymes closely linked to starch and sucrose metabolism could be detected in the leaves expressing ASPP in the cytosol. The overall results show that, essentially similar to cereal endosperms, most of the ADPG linked to starch biosynthesis in source leaves occurs in the cytosol.

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Localization of Carbohydrate Metabolizing Enzymes in Guard Cells of Commelina communis

Cited by 27 publications

References 27 publications

Amylases in Pea Tissues with Reduced Chloroplast Density and/or Function

Amylases in Pea Tissues with Reduced Chloroplast Density and/or Function

Sugar Concentrations in Guard Cells of Vicia faba Illuminated with Red or Blue Light

Most of ADP·glucose linked to starch biosynthesis occurs outside the chloroplast in source leaves

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