Results of the hormone square and comparison with other data

Our hormone square showed the following development:

Auxin IBA→   Cytokinin BAP ↓	0 mg/l	0.02 mg/l	0.2   mg/l	2 mg/l
0 mg/l	1. Very long roots, no ramification, no callus, no fresh shoots	2. Very long roots but less than in nr.9, very little ramification, no callus, no fresh shoots	3. Similar to nr.4 but less rooting and a bit less callus	4. Dark, brown large callus, but many roots with ramifications
0.02 mg/l	5. Only little rooting, very little callus, no fresh shoots, but healthy	6. Little callus (also internodes), little rooting but some ramification, not too long	7. Little rooting, thin and young roots, green callus, healthy leaves	8. Callus, very compact, brown and green, little shoots in internodes, root ramification
0.2 mg/l	9. Very long roots, less than in nr.1, little ramification, no callus, no fresh shoots	10. some green callus, no roots, few little shoots growing from internodes	11. big green callus, no roots, little shoots growing from internodes	12. big green callus, no roots, little shoots growing from internodes, plantlets smaller
2 mg/l	13. some green callus, no roots, many shoots growing, plantlets smaller, stressed	14. some green callus, no roots, very many shoot growing from internodes, real proliferation, stressed	15. same as 14.	16. even larger green callus, no roots, less shoots growing from internodes

We tried to make a meaningful ranking for the roots and another one for the shoots. In order to do the ranking, we considered the qualities which would be most beneficial and which promise a good fitness if the explants were used for a transfer into in vivo conditions.

So concerning the roots, we determined that the explants already need to have some. This is essential for a quick adaption to taking up water and nutrients from the soil and quickly get good foothold. Even though the roots developed in the container can’t really be used in in vivo conditions, new ones can establish quickly if there is already some rooting. However, the explants from the containers in which the most roots had developed were almost too old. In Nr. 3, 4 and 8 there was very much rooting, but the roots were already very long and did not ramify much.

We thought it better to take plantlets in a stage of young roots, so that they will ramify a lot when cut and transferred into soil. In addition to that, direct rooting is better than when there's callus formed in between. Therefore, Nr. 5, 6 and 7 were considered as more suitable.

Concerning the shoots, the highest activity and cell division was found in high cytokinin (BAP) concentrations, where many little leaves were proliferating even from the internodes. Nevertheless, we regarded only well grown and vigorous shoots as desirable. If the internodes were very short, leaves were light green and overall the plantlets looked stressed, the ranking was low (this was the case in high concentrations of BAP). The best shoots could be found in Nr. 7 and 9.

Therefore, regarding both, roots and shoots the best hormone mix could be found in Nr. 7 with 0.02 mg/l BAP and 0.2 mg/l IBA. Also good plantlets in regard to suitability for in vivo conditions could be found in Nr. 5, 3 and 9.

The other group also found the most intensive rooting in Nr. 3, 4 and 8, yet also in Nr.12. Since this group probably didn’t define the ranking in regard to suitability for a transfer to in vivo conditions, they regarded these as the best ones.

This result is in accordance with scientific findings. Auxin is known to stimulate root growth, but rather in concentrations higher than 0.2 mg/l and not if there’s too much cytokinin.

On the other hand, the ranking of shoots looks completely different. This group counted the shoots on leaves and on stems of leaves. The best hormone combination for a good shoot formation was found to be 0.2 or 2 mg/l kinetin and 0.02 mg/l NAA. These were containers Nr. 10 and 14.

In any case, the effect of a combination of auxin and cytokinin was clearly visible in both. Some differences between the two hormone squares might also be due to the use of different plant hormones in both groups or just due to some mistakes in the preparation of the mixtures.

It was difficult to find some scientific reference, even though various studies on different combinations of auxins and cytokinins had been carried out in the past (two of them mentioned below, but which couldn’t be accessed). Since I’ve already spent too much time on this research and read too many unsuitable abstracts of papers, I will stop here. However, from what I’ve read and learned, our result shows the very expected effects. The auxin is stimulating roots, if it isn’t drowned by too high cytokinin concentrations. The cytokinin strongly stimulates cell division of the overground parts, which in our hormone square is best visible in the internodes.

References:

James, D., & Newton, B. (kein Datum). AUXIN: CYTOKININ INTERACTIONS IN THE IN VITRO MICRO-PROPAGATION OF STRAWBERRY PLANTS.

Karakullukçu, S., Agaoglu, Y., & Abak, K. (kein Datum). EFFECT OF DIFFERENT AUXIN-CYTOKININ COMBINATIONS ON THE IN VITRO PROPAGATION OF RASPBERRY CV. SCHÖNEMANN.