Biology 52 problem set D: Plant development, meristems, flowers

(*hand in answers in recitation)

35) How do plants manage to grow despite having a cell wall? What biochemical functions stimulate plant cell growth?

36) Indicate the meristems on the following diagram of a plant. Label the different types. Indicate which meristem(s) will produce leaves, branches, flowers, and lateral roots.

*37) If the top of a plant (including the shoot apical meristem) is chopped off, some lateral meristems that had been dormant will begin to grow. One way to explain this finding is to hypothesize that an intercellular signal controls lateral meristem growth. Based on this result,

a) Which cells send the signal?

b) Which cells respond to the signal?

c) What instruction does this signal convey to the cells that receive it?

d) A student suspects that the plant hormone auxin is the signal. Suggest an experiment that will allow one to test whether auxin is sufficient to produce the response.

38) The following diagram indicates the expression domains of the CLV1 and CLV3 genes in a wild-type meristem. The CLV1 gene encodes a receptor kinase, and the CLV3 gene encodes a small peptide.

a) Indicate which cells are dividing most rapidly in this meristem.

b) What are the probable biochemical functions of i) the CLV1 protein and ii) the CLV3 protein?

c) What is the phenotype of a clv1 mutant? Include in your answer which cells are affected.

d) clv1 and clv3 mutants have the same phenotypes, and therefore the two genes are thought to act in the same regulatory pathway. What is the function of this pathway in meristem organization?

39) a) On the following diagram of a plant ovule, label the egg, the synergids, the central cell, and the chalazal cells. b) Indicate which cells will be fertilized by male gametes. c) Indicate which cells will become the embryo, the endosperm, and the seed coat.

40) A particular plant species normally has a brown seed coat and a purple endosperm. A single recessive mutation confers a yellow seed coat and a yellow endosperm when homozygous. A plant that is homozygous for this recessive mutation is fertilized with pollen from a plant homozygous for the wild-type gene at this locus (i.e. the male parent makes a brown seed coat and purple endosperm).

a) What color will the seed coat be in the F1 seed deriving from this cross?

b) What color will the endosperm be in the same F1 seed?

c) What color will the seed coat be in F2 seed derived from self-fertilization of the F1 plants in part a)?

d) What color will the endosperm be in the F2 seed?

41) What organs would form in the four whorls of flowers of Arabidopsis plants of the following genotypes:

genotype whorl 1 whorl 2 whorl 3 whorl 4

wild type

agamous

pistillata