INTERNODE LENGTH IN PISUM: EFFECT OF THE GENE art (arthritic)

PNL Volume 19 1987 RESEARCH REPORTS 59

Rothwell, R. N. and I. C. Murfet

Botany Dept., University of Tasmania
Hobart 7001, Australia

The gene art (arthritic) is characterized by the presence of
swollen nodes, undulate leaves and stipules, and a marked fore-
shortening of the upper internodes (2). The latter effect is
clearly shown by the results in Table 1 obtained from two near-
-isogenic tall (Le/Le) F5 progenies [B584-705-(2) and (4)] which
were segregating for the Art-art pair of alleles. A significant
reduction in the internode length of art segregates was already
apparent in the lower internodes, e.g. internode 5 was 26% shorter
in art than Art segregates. (Internode 5 is defined here as lying
between nodes 5 and 6 counting from the lowest scale leaf as node
1). As noted by Marx (2) the reduction was even greater in the
upper portion of the stem, and for the internode two below the
first flower (internode 17 or 18 in this case) the art segregates
were 40% shorter than their Art counterparts. There was a dis-
tinct difference in final height between the two genotypes (Fig.
1) with art segregates attaining an average only two-thirds the
final height of Art segregates. The two genotypes flowered at the
same node (both means 19.4) and they produced an almost identical
number of internodes (art 22.4 and Art 22.1). Hence in this case
the difference in final height truly reflects the cumulative ef-
fect of the difference in internode length.

We examined the anatomical basis for the difference in inter-
node length between Art and art plants using the epidermal strip
technique (1). Length measurements were made for 10 epidermal
cells and 30 outer cortical cells per internode per plant. Corti-
cal cells were measured in sets of three. Cell numbers per inter-
node were estimated by dividing the length of an internode by the
mean cell length for that internode.

A similar anatomical pattern emerged regardless of the inter-
node or cell type considered (Table 1). It is clear that the re-
duction in internode length in art, segregates was wholly attri-
butable to a marked reduction in the number of cells per inter-
node. Cell length was in fact slightly greater in art segregates
than Art segregates but the difference did not attain statistical
significance in the present study. However, the consistency of
the effect across cell type and internode position suggests that
it may have proved significant if a larger sample size had been
used. The results for art contrast with those obtained for the
internode length mutants le and na (3) and lk (4) where the
reduction in internode length was found to be associated in each
case with a marked decrease in both cell number and cell length.

Acknowledgement. We are indebted to Prof. G. A. Marx, NYS
Agricultural Experiment Station, Geneva, NY, for providing seed of
the progenies used and for drawing our attention to the effect of
art on internode length.

60 PNL Volume 19 1987 RESEARCH REPORTS

1. Arney, S. E. and P. Mancinelli. 1966. New Phytologist
65:161-175.

2. Marx, G. A. 1981. PNL 13:38-39.

3. Reid, J. B. , I. C. Murfet. and W. C. Potts. 1983. J. Exp.
Bot. 34:349-364.

4. Ross, J. J. and J. B. Reid. 1986. Physiologia Plantarum
67:673-679.

Fig. 1. Distribution of final height for art/art and Art/-
segregates in F₅ progenies B584-705-(2) and (4).
All plants were tall (Le/Le) .

Table 1. Effect of the Art - art gene difference on internode length and on the length
_and number of epidermal and outer cortical cells._


Genotype	Internode	Stem length (mm)		Epidermal cells				Cortical cel1s
		Stem length (mm)		Length (urn)		Number		Length(mkm)		Number
		Mean	S.E.	Mean	'S.E.	Mean	S.E.	Mean	S.E.	Mean	S.E.
Art/-	5	65.8	0.9	384	18	173	6	125	3	528	1 7
art/art	5	48.4***	2.8	424	29	116**	9	134	1 3	368***	25
Art/-	17 or 18^�	132.4	12.5	304	19	439	45	91	7	14 59	126
art/art	17 or 18^�	78.8**	3.6	324	17	247**	23	106	1	745***	25

** *** - Difference between the Art/- and art/art means significant at the 0.01 or 0.001 level,
respectively.

� - The internode two below the first flower. (Flowering commenced at node 19 or 20.)

The data were obtained from 5 Art/- and 5 art/art segregates in two near-isogenic tall (Le
F5 progenies. Plants were grown one per 14 cm slimline pot under an 18 h photoperiod.

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