Higher plants pass through several phases of shoot growth during which they may produce morphologically distinct vegetative structures. In Arabidopsis thaliana this phenomenon is apparent in the distribution of trichomes on the leaf surface. Leaves produced early in rosette development lack trichomes on their abaxial (lower) surface, leaves produced later have trichomes on both surfaces, and leaves in the inflorescence (bracts) may have few or no trichomes on their adaxial (upper) surface. Here we describe some of the factors that regulate this distribution pattern. We found that the timing of abaxial trichome production and the extent to which bracts lack adaxial trichomes varies in different ecotypes. The production of abaxial trichomes appears to be regulated by the age, rather than the size of the plant. This conclusion is based on the observation that mutations that affect either the rate (altered meristem programming1) or onset (paused) of leaf initiation respectively increase or decrease the number of leaves that lack abaxial trichomes, but have only a minor effect on the time at which the first leaf with abaxial trichomes is produced. The production of abaxial trichomes is coordinated with the reproductive development of the shoot as this trait is delayed by photoperiodic conditions and some mutations that delay flowering. The loss of adaxial trichomes is likely to be a consequence of floral induction, and is accelerated by terminal flower1-10, a mutation that accelerates inflorescence development. We demonstrate that gibberellins promote trichome production in Arabidopsis and present evidence indicating that abaxial trichome production is regulated by both the level of a trichome inducer and the competence of the abaxial epidermis to respond to this inducer.

REFERENCES

Brand
M. H.
,
Lineberger
R. D.
(
1992
)
In vitro rejuvenation of Betulaceae: morphological evaluation.
Am. J. Bot
79
,
618
625
Chaudhury
A. M.
,
Letham
S.
,
Craig
S.
,
Dennis
E. S.
(
1993
)
amp1 -a mutant with high cytokinin levels and altered embryonic pattern, faster vegetative growth, constitutive photomorphogenesis and precocious flowering.
Plant J
4
,
907
916
Chien
J. C.
,
Sussex
I. M.
(
1996
)
. Differential regulation of trichome formation on the adaxial and abaxial leaf surfaces by gibberellins and photoperiod in Arabidopsis thaliana (L.) Heynh.
Plant Physiol
111
,
1321
1328
Coen
E. S.
,
Meyerowitz
E. M.
(
1991
)
The war of the whorls: Genetic interactions controlling flower development.
Nature
353
,
31
37
Evans
M. M. S.
,
Passas
H.
,
Poethig
R. S.
(
1994
)
Heterochronic effects of glossy15 mutations on epidermal cell identity in maize.
Development
120
,
1971
1981
Evans
M. M. S.
,
Poethig
R. S.
(
1995
)
Gibberellins promote vegetative phase change and reproductive maturity in maize.
Plant Physiol
108
,
475
487
Gilmour
S. J.
,
Zeevaart
J. A. D.
,
Schwenen
L.
,
Graebe
J. E.
(
1986
)
Gibberellin metabolism in cell-free extracts from spinach leaves in relation to photoperiod.
Plant Physiol
82
,
190
195
Hempel
F. D.
,
Feldman
L. J.
(
1994
)
Bi-directional inflorescence development in Arabidopsis thaliana: Acropetal initiation of flowers and basipetal initiation of paraclades.
Planta
192
,
276
286
Hou
Y.
,
von Arnim
A. G.
,
Deng
X. W.
(
1993
)
A new class of Arabidopsis constitutive photomorphogenic genes involved in regulating cotyledon development.
Plant Cell
5
,
329
339
Hulskamp
M.
,
Misera
S.
,
Jurgens
G.
(
1994
)
Genetic dissection of trichome cell development in Arabidopsis.
Cell
76
,
555
566
Jacobsen
S. E.
,
Olszewski
N. E.
(
1993
)
Mutations in the SPINDLY locus of Arabidopsis alter gibberellin signal transduction.
Plant Cell
5
,
887
896
Koornneef
M.
,
van der Veen
J. H.
(
1980
)
Induction and analysis of gibberellin sensitive mutants in Arabidopsis thaliana (L.) Heynh. Theor. Appl.
Genet
58
,
257
263
Koornneef
M.
,
Elgersma
A.
,
Hanhart
C. J.
,
Van Loenen-Martinet
E. P.
,
Van Rijn
L.
,
Zeevaart
J. A. D.
(
1985
)
A gibberellin insensitive mutant of Arabidopsis thaliana.
Physiol. Plant
65
,
33
39
Larkin
J. C.
,
Young
N.
,
Prigge
M.
,
Marks
M. D.
(
1996
)
The control of trichome spacing and number in Arabidopsis.
Development
122
,
997
1005
Lawson
E.
,
Poethig
R. S.
(
1995
)
Shoot development in plants: time for a change.
Trends Genet
11
,
263
268
Martínez-Zapater
J. M.
,
Jarillo
J. A.
,
Cruz-Alvarez
M.
,
Roldán
M.
,
Salinas
J.
(
1995
)
Arabidopsis late-flowering fve mutants are affected in both vegetative and reproductive development.
Plant J
7
,
543
551
Medford
J. I.
,
Behringer
F. J.
,
Callos
J. D.
,
Feldmann
K. A.
(
1992
)
Normal and abnormal development in the Arabidopsis vegetative shoot apex.
Plant Cell
4
,
631
643
Moose
S. P.
,
Sisco
P. H.
(
1994
)
Glossy15 controls the epidermal juvenile-to-adult transition in maize.
Plant Cell
6
,
1343
1355
Pharis
R. P.
,
Evans
L. T.
,
King
R. W.
,
Mander
L. N.
(
1987
)
Gibberellins, endogenous and applied, in relation to flower induction in the long-day plant Lolium temulentum.
Plant Physiol
84
,
1132
1138
Poethig
R. S.
(
1990
)
Phase change and the regulation of shoot morphogenesis in plants.
Science
250
,
923
930
Schaffalitzky de Muckadell
M.
(
1954
)
Juvenile stages in woody plants.
Physiol. Plant
7
,
782
796
Shannon
S.
,
Meeks-Wagner
D. R.
(
1991
)
A mutation in the Arabidopsis TFL1 gene affects inflorescence meristem development.
Plant Cell
3
,
877
892
Shannon
S.
,
Meeks-Wagner
D. R.
(
1993
)
Genetic interactions that regulate inflorescence development in Arabidopsis.
Plant Cell
5
,
639
655
Sun
T.
,
Goodman
H. M.
,
Ausubel
F. M.
(
1992
)
Cloning the Arabidopsis GA1 locus by genomic subtraction.
Plant Cell
4
,
119
128
Weigel
D.
,
Alvarez
J.
,
Smyth
D. R.
,
Yanofsky
M. F.
(
1992
)
LEAFY controls floral meristem identity in Arabidopsis.
Cell
69
,
843
859
Weigel
D.
,
Meyerowitz
E. M.
(
1994
)
The ABCs of floral homeotic genes.
Cell
78
,
203
209
Weigel
D.
,
Nilsson
O.
(
1995
)
A developmental switch sufficient for flower initiation in diverse plants.
Nature
377
,
495
500
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