Pyrimidine Metabolism in <i>Lemna minor</i>

Frick, Hugh

doi:10.1104/pp.61.6.989

Cited by 4 publications

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“…Plastids 5 and 6 are continuous through frames e and f. These plastids are among the largest observed in Cdr-bleached cells. Note Our results are consistent with those reports describing varying plastid numbers according to cell size (2,6,13,20), and consistent with the proposition that Cdr inhibits the replication of plastids during development of mesophyll cells in Lemna (9). The average depth per plastid in Lemna (about 7.5 um, (13) extended these studies to the numbers and size distribution of mesophyll chloroplasts in some 10 genera of angiosperms.…”

Section: Resultssupporting

confidence: 92%

“…

ABSTRACTShort term photoheterotrophic growth of Lemna minor in the presence of 100 micrograms per milliliter (440 micromolar) cytidine deoxyriboside bleaches the fronds in the absence of effect upon growth rate (Frick 1978 Plant Physiol 61: 989-992). Serial sections of mesophyll cells of green and bleached fronds were compared in the Ught microscope.

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mentioning

confidence: 99%

“…The natural metabolite, cytidine deoxyriboside, quantitatively induces bleaching in the fronds of photoheterotrophically growing Lemna minor (duckweed) when it is present in the medium in high concentrations (440 uM), and does so without inhibiting growth measured as frond multiplication (9). The bleaching induced by Cdr2 is fully prevented by Tdr, Cr, or Ur, but is not affected by orotic-acid, Udr, or any purine riboside tested.…”

mentioning

confidence: 99%

“…Either the number ofintact chloroplasts per cell is reduced through Cdr inhibition of plastid replication, or the same number of plastids is present in bleached cells and each is structurally damaged (10 case, regreening of previously bleached fronds after removal of the plants from Cdr occurs (9), and this could come about by division of proplastids in the first alternative or by repair of damaged plastids in the second alternative.…”

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confidence: 99%

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Pyrimidine Metabolism in Lemna minor

Pizzolato¹,

Frick²

1979

Plant Physiol.

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Short term photoheterotrophic growth of Lemna minor in the presence of 100 micrograms per milliliter (440 micromolar) cytidine deoxyriboside bleaches the fronds in the absence of effect upon growth rate (Frick 1978 Plant Physiol 61: 989-992). Serial sections of mesophyll cells of green and bleached fronds were compared in the Ught microscope. The number of plastids in cells of comparable size was reduced during bleaching by more than 50%. The total and average plastid profile area per section in the series was reduced on the order of 70%, and the summed plastid profile area over the entire cell was reduced about 90%. Thus, cytidine deoxyriboside-bleached mesophyll cells contained fewer identifiable plastids (50%) of smaUler volume (10-30%) than the green control cells.The natural metabolite, cytidine deoxyriboside, quantitatively induces bleaching in the fronds of photoheterotrophically growing Lemna minor (duckweed) when it is present in the medium in high concentrations (440 uM), and does so without inhibiting growth measured as frond multiplication (9). The bleaching induced by Cdr2 is fully prevented by Tdr, Cr, or Ur, but is not affected by orotic-acid, Udr, or any purine riboside tested. Our working assumption is that Cdr in some way interferes specifically with plastic DNA biosynthesis and thereby with chloroplast biogenesis. This ability of Cdr to induce phenocopies of Chl-deficient mutants without affecting growth rate implies a functional compartmentation of pyrimidine metabolism between chloroplast and whole cell which could be manifest by several mechanisms.The ontogeny of the monocotyledenous hydrophyte L. minor is such that within each visible frond of dimensions of about 3 x 5 mm are included the frond primordia for at least two further generations (10, 25), which elongate during growth with an orientation approximately normal to the parental frond (Fig. 1). Cells in all stages of differentiation may be encountered within the area of a few microscopy sections (10).The case, regreening of previously bleached fronds after removal of the plants from Cdr occurs (9), and this could come about by division of proplastids in the first alternative or by repair of damaged plastids in the second alternative. MATERIALS AND METHODSCultures of L. minor were grown axenically for 8 days at 25 + 2 C in continuous 400 ltE m-2 s-' mixed cool-white fluorescent and incandescent irradiation in the 400 to 700 nm region on photoheterotrophic medium (9) with or without 100 ,ug/ml Cdr (440 AM). Mother fronds of control and bleached three-frond clones were razor-trimmed approximately 500,um from the distal tip. Clones with fully bleached daughers were fixed at room temperature for 48 h in 6.5% glutaraldehyde (0.4 M phosphate buffer, pH 7.0), dehydrated through ethanol and propylene oxide, and embedded in modification E of Spurr's epoxy resin (27). Transverse l-,m serial sections of the eldest daughters (about 2 mm long) were cut with a Sorvall (Porter Blum) MT-1 ultramicrotome parallel to the long axis of the mother...

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