Response to amino acids and vitamins by excised maize inbred and hybrid embryos cultured in vitro.

Through the use of aseptic techniques (described in Bot. Gaz. 112:52‑57) the effect of 10 amino acids and 4 B vitamins on growth of young seedlings grown from excised embryos of Inbreds 38‑11, K64, and WF9 and their reciprocal hybrids was measured. The amino acids were added at final concentrations of M/5000 to artificial culture medium and the vitamins were added at the rate of 2 p.p.m. This method whereby the young embryos are divorced very early from their endosperm reserves and grown on a chemically defined medium should simplify the investigation of certain metabolic processes in maize. The objective of these experiments was to determine if any relationship exists between the effects of these growth substances and heterosis.

Due to the small number of replications and the high degree of variability (coefficients of variability commonly ranged from 40‑60%), statistical significance could not be shown for many of the differences between growth on control medium and that on supplemented media. However, certain of these differences seemed consistent enough to indicate biological significance. A response by increased growth was shown by some strains but not by others to certain of the growth substances. Moreover, these differences in response were fairly constant between inbred and hybrid strains. Therefore, some of the data seem to serve as a possible clue to the biochemical basis of heterosis.

In some cases inbred lines showed a response to a particular supplement and hybrids involving these strains also showed increase growth on media supplemented with the same substance. This result was obtained with the amino acid arginine. In almost all cases Inbred 38‑11, as well as the hybrids involving it, responded to arginine by showing increased growth. In some of the cases this response was statistically significant. On the other hand, Inbred WF9 made no response to arginine and Inbred K64 showed a non-significant increased growth in those cultures receiving arginine in only one of two groups of data. The hybrid between the latter two inbreds showed no response to arginine. Representative data are shown in the accompanying table.

Thiamin promoted better growth for Inbred WF9 while neither of the other inbreds showed a response to this vitamin. The hybrids involving WF9 as the maternal parent also showed a response to thiamin. Tryptophane seemed stimulatory only to K64 of the inbreds while hybrids involving it showed increased growth on media supplemented with this substance.

These data were interpreted to mean that the inbreds transmit to their hybrid seedlings the ability for increased utilization of the particular metabolites. It would be desirable to relate determinations of the amounts of these substances in the endosperm with the above type of data.

Some of the data seemed to be interpreted best on the basis that hybrid superiority results from the ability of the hybrid to synthesize certain of the metabolites in greater quantities than their component inbreds. In these cases inbred parents showed better growth on media supplemented with certain growth substances while their hybrids showed no response to these same supplements. This result was obtained with riboflavin. Inbreds 38‑11 and K64 showed increased growth on media supplemented with this substance while neither of the reciprocal hybrids between them showed a response to it. WF9, on the other hand, showed no response to this supplement.

Further data involving greater numbers of replications is needed before conclusions can be drawn from these experiments. It might also be desirable to determine the effects of these amino acids and vitamins when added in groups. More experiments of this type are planned.

Table I

Effect of arginine on growth in 10 days by maize inbred and hybrid embryos.

Maize Inbreds or Hybrids	Age in Days of Embryo When Excised	No. of Replications	Mean Dry Weights of Seedlings in mg.
			Control (No Supplement)	Control + Arginine (M/5000)
WF9 �	18	5	8.6 � 1.4	8.9 � 0.7
HF9 x K64	18	10	8.1 � 1.0	7.2 � 1.2
K64 �	18	5	6.3 � 1.8	8.0 � 0.9
K64 x 38‑11	18	5	10.4 � 3.2	9.6 � 0.5
38‑11 x K64	18	5	7.3 � 1.1	11.1 � 2.6
38‑11 �	18	5	6.2 � 0.4	11.3 � 1.7
38‑11 �	19	4	9.0 � 0.2	10.8 � 0.5
38‑11 x WF9	19	4	14.6 � 1.8	16.7 � 1.9
38‑11 �	21	4	24.0 � 2.4	14.5 � 1.7
WP9 x 38‑11	21	10	15.7 � 1.6	20.1 � 2.3

James E. Wright, Jr.