TY - JOUR
T1 - Expression of the phloem lectin is developmentally linked to vascular differentiation in cucurbits
AU - Dannenhoffer, Joanne M.
AU - Schulz, Alexander
AU - Skaggs, Megan I.
AU - Bostwick, Dwight E.
AU - Thompson, Gary A.
N1 - Funding Information:
The authors thank the W. Atlee Burpee Company, Warminster, Pa. for kindly donating the seed for these studies and Mr. Mike Fremarek for photographic assistance. We also thank Dr. Dinkar D. Sabnis (University of Aberdeen, UK) and Dr. M. Carol Alosi (University of California, Berkeley, USA) for the antibodies that were used in the immunocytochemical localization studies. This research was supported in part by grant No. 92–37304–8007 from the U.S. Department of Agriculture Cooperative State Research Service, USA to G.A.T., grant No. IBN-9422615 from the National Science Foundation Integrative Plant Biology Program, USA to G.A.T. and grant No. Schu 617/1–3,1–4 from the Deutsche Forschungsgemeinschaft, Germany to A.S.
PY - 1997
Y1 - 1997
N2 - The conducting elements of phloem in angiosperms are a complex of two cell types, sieve elements and companion cells, that form a single developmental and functional unit. During ontogeny of the sieve element/companion cell complex, specific proteins accumulate forming unique structures within sieve elements. Synthesis of these proteins coincides with vascular development and was studied in Cucurbita seedlings by following accumulation of the phloem lectin (PP2) and its mRNA by RNA blot analysis, enzyme-linked immunosorbent assay, immunocytochemistry and in situ hybridization. Genes encoding PP2 were developmentally regulated during vascular differentiation in hypocotyls of Cucurbita maxima Duch. Accumulation of PP2 mRNA and protein paralleled one another during hypocotyl elongation, after which mRNA levels decreased, while the protein appeared to be stable. Both PP2 and its mRNA were initially detected during metaphloem differentiation. However, PP2 mRNA was detected in companion cells of both bundle and extrafascicular phloem, but never in differentiating sieve elements. At later stages of development, PP2 mRNA was most often observed in extrafascicular phloem. In developing stems of Cucurbita moschata L., PP2 was immunolocalized in companion cells but not to filamentous phloem protein (P-protein) bodies that characterize immature sieve elements of bundle phloem. In contrast, PP2 was immunolocalized to persistent P-protein bodies in sieve elements of the extrafascicular phloem. Immunolocalization of PP2 in mature wound sieve elements was similar to that in bundle phloem. It appears that PP2 is synthesized in companion cells, then transported into differentiated sieve elements where it is a component of P-protein filaments in bundle phloem and persistent P-protein bodies in extrafascicular phloem. This differential accumulation in bundle and extrafascicular elements may result from different functional roles of the two types of phloem.
AB - The conducting elements of phloem in angiosperms are a complex of two cell types, sieve elements and companion cells, that form a single developmental and functional unit. During ontogeny of the sieve element/companion cell complex, specific proteins accumulate forming unique structures within sieve elements. Synthesis of these proteins coincides with vascular development and was studied in Cucurbita seedlings by following accumulation of the phloem lectin (PP2) and its mRNA by RNA blot analysis, enzyme-linked immunosorbent assay, immunocytochemistry and in situ hybridization. Genes encoding PP2 were developmentally regulated during vascular differentiation in hypocotyls of Cucurbita maxima Duch. Accumulation of PP2 mRNA and protein paralleled one another during hypocotyl elongation, after which mRNA levels decreased, while the protein appeared to be stable. Both PP2 and its mRNA were initially detected during metaphloem differentiation. However, PP2 mRNA was detected in companion cells of both bundle and extrafascicular phloem, but never in differentiating sieve elements. At later stages of development, PP2 mRNA was most often observed in extrafascicular phloem. In developing stems of Cucurbita moschata L., PP2 was immunolocalized in companion cells but not to filamentous phloem protein (P-protein) bodies that characterize immature sieve elements of bundle phloem. In contrast, PP2 was immunolocalized to persistent P-protein bodies in sieve elements of the extrafascicular phloem. Immunolocalization of PP2 in mature wound sieve elements was similar to that in bundle phloem. It appears that PP2 is synthesized in companion cells, then transported into differentiated sieve elements where it is a component of P-protein filaments in bundle phloem and persistent P-protein bodies in extrafascicular phloem. This differential accumulation in bundle and extrafascicular elements may result from different functional roles of the two types of phloem.
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U2 - 10.1007/s004250050083
DO - 10.1007/s004250050083
M3 - Article
AN - SCOPUS:0030901599
SN - 0032-0935
VL - 201
SP - 405
EP - 414
JO - Planta
JF - Planta
IS - 4
ER -