Comparison of Seed Coat Development and Composition in Normal and Hull-less Strains of Pumpkin (Cucurbita pepo L.)

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Cucurbit Genetics Cooperative Report 5: 51-52 (article 25) 1982

S.G. Stuart and J.B. Loy
University of New Hampshire, Durham, NH 03824

Pumpkin seeds normally develop a well-defined, five-zoned seed coat or testa (1) by ten to fifteen days post-anthesis (2). In 1934, Tschermak-Seysenegg reported a ‘naked-seeded’ or hull-less mutant in pumpkin which did not develop a distinctly organized testa. All seed coat tissue layers are present in the hull-less phenotype, however, all layers collapse during tissue desiccation of mature seeds. Early investigators attributed tissue collapse to a failure of mutant cell walls to lignify during seed coat development (3, 4). Celluloses and non-cellulosic polysaccharides comprise a substantial proportion of the seed coat of Cucurbita pepo (5). Therefore, it appeared relevant to compare more critically by biochemical and histochemical analyses, the seed coat composition of hull-less mutant and normal seeds of C. Pepo.

Analyses of seed coat composition of two normal strains, cvs. ‘Small Sugar’ and ‘Jack O’Lantern’, and two hull-less mutant strains, cvs. ‘Tricky Jack’ and ‘293A, of pumpkin revealed a marked reduction of lignin, structural polysaccharides and protein, and increased amounts of ethanol-soluble substances and lipids in hull-less cultivars compared to normal cultivars (Table 1). Testae from hull-less seeds weighed roughly 57 percent less than those from seeds of the normal strains.

Table 1. Seed coat composition (mg/testa) of mature desiccated seeds of normal and hull-less strains of C. pepo.

Normal Strain

Mutant Strain

Component

‘Small Sugar’

‘JackO’Lantern’

‘Tricky Jack’

‘239A’
80% ethanol soluble 1.1 O.9 2.0 1.7
Lipids / pigments 0.3 0.7 0.8 0.9
Lignin 5.6 5.0 1.0 0.8
Protein 4.0 3.8 1.8 1.8
Structural polysaccharides a 8.8 9.4 3.4 2.9
TOTAL 19.8 19.8 9.0 8.1

a This fraction includes cellulose, hemicelluloses and pectic polymers.

Histological studies indicated a deficiency in secondary cell wall development in hull-less mutant testae as early as ten days post-anthesis. Starch granules, presumed to function as precursor molecules for cell wall synthesis, were abundant in both mutant and normal testae early in development.

We suggest that the marked reduction in lignin in hull-less mutant testae may be a secondary phenomenon resulting from a deficiency in the polysaccharide matrix which is a prerequisite for lignin formation.

Literature Cited

  1. Singh, D. and A.S.R. Dathan. 1972. Structure and development of seed in cucurbitaceae. VI. Seeds of Cucurbita. Phytomorphology 22:29-45.
  2. Stuart, S.G. 1981. Comparative studies of testa development in normal and hull-less seeded strains of Cucurbita pepo L. MS Thesis, University of New Hampshire, Durham, N.H.
  3. Heinisch, O. and M. Ruthenberg. 1950. Die Beduntung der Samenschale fur die Zuchtung des Olkurbis. Pflanzen. 29:159-174.
  4. Dreher, M.L., C.W. Weber, W.P. Bemis and J.W. Berry. 1980. Cucurbit seed coat composition. J. Agric. Food Chem. 28:354-366.